Professor Huxley, F.R.S.–This gentleman will resume his course of twenty-four lectures on "The Structure and Classification of the Mammalia," in the theatre of the Royal College of Surgeons, on Tuesday next, commencing with the Zoological Anatomy of Man, with especial reference to the bony skeleton and the muscles; the resemblance and difference of the pectoral and pelvic limbs; the characters and the nomenclature of the teeth; the brain and the organs of sense and voice; the organs of reproduction, and the process of development; variations of structure.–The Comparative Anatomy of the Apes and Lemurs–The Insectivora, Cheiroptera, and Rodentia–Remarks upon the Classification of the preceding groups–The Carnivora–The Ungulate Mammals–The Sirenia, Cetacea, and Edentata–The Proboscidea and the genus Hyrax–Remarks upon the Classification of the preceding groups–The Marsupialia–The Monotremata–Remarks upon the Classification of the Mammalia generally.

[153]

After a few introductory remarks, Professor Huxley stated that further observation and reflection had served to convince him more fully of the truth of the tripartite division of the vertebrate sub-kingdom, which he had announced in the lectures delivered at the College last year. The first section or province (Ichthyopsida ), containing the fish and the Amphibia, all possess, he said, branchial respiratory organs, at least at some period of their existence: in the embryonic condition they are without amnion, and the allantois is absent or rudimentary, their blood corpuscles are nucleated, and their lower jaw does not articulate directly with the skull. The members of the second province, comprising the classes Reptilia and Aves (Sauropsida ), never possess branchiæ; have the amnion and allantois well developed, the latter generally taking on a respiratory function; their blood-corpuscles are nucleated; each ramus of the lower jaw is composed of several pieces, and articulates by means of the quadrate bone with the skull; they have a single occipital condyle, and the appendages of their epidermis take the form of scales or feathers. The third division contains the Mammalia alone; these never have branchiæ; the amnion and allantois are always developed; the large majority of their blood-corpuscles are non-nucleated; each ramus of the lower jaw is simple, and articulates with the squamosal element of the skull; there are two occipital condyles; the epidermal appendages are in the form of hair, and the females have mammary glands. As far as our present knowledge extends, both of living and extinct vertebrate animals, these three great groups are absolutely defined in nature; while, on the other hand, between fish and amphibia, birds and reptiles, respectively, numerous points of affinity may be found.

The class Mammalia being the subject of the present course, Man, as the form with whose anatomy most of the audience were best acquainted, was selected as a type, and a sketch of the salient points of his structure was given first, to assist in following out in subsequent lectures the various modifications of organisation found in other mammals. The lecturer commenced a description of what he termed the "zoological anatomy of man" (having especial reference to those parts which offer the best terms of comparison in descending through the mammalian series) by stating that which first strikes [154] the most superficial observer of the human body, is the erect attitude. This alone, however, is not distinctive; it is shared by the penguin and kangaroo, but in these animals the body is suspended on the flexed femur; the vertical trunk placed on an extended hind-limb is peculiar to man. The principal remaining external zoological characters of man are–the plantigrade sole, the backward arching of the spine in the dorsal region, the hollow in the lumbar region, the wide chest, the muscular prominence formed by the powerful abductors of both pairs of limbs, and the peculiar proportions of the body, the length from tip to tip of extended anterior extremities equaling the height, the vertical central point being a little below the symphysis pubis, the whole height being seven or eight times the vertical height of the head, the legs being longer than the arms, and the proximal segments of both limbs longer than the distal. The pollex is perfectly free and opposable, and does not lie in the same plane as the other fingers; the palm is very nearly square; the carpus is shorter than the metacarpus, this shorter than the digits; the forearm capable of free rotation. In the lower limbs, the hallux is only imperfectly mobile, and scarcely at all opposable, and lies nearly in the same plane as the other toes; the second toe is generally the longest; the sole is longer than broad; the tarsus longer than the metatarsus, this longer than the digits; there is more or less union by integument or "syndactyly" of the three middle toes. One of the greatest peculiarities of the human body is the distribution of hair upon its surface; on the head this is more abundant on the dorsal than the anterior aspect, on the body more developed in front than behind, on the limbs more on the extensor than the flexor surfaces, without relation to front or back. The nails are comparatively flat, and do not cover the whole surface of the phalanx on which they rest. The septum of the nose is narrow and elongated, causing the external projection of the organ; the nostrils are directed downwards. The penis is pendulous, the testes contained in a well-developed scrotum placed behind the root of the penis, the perinæum is distinct, and the mammæ are pectoral.

The special zoological characters of the human skeleton are as follows:–The spinal column consists of thirty-three vertebræ, of which seven are cervical, twelve dorsal, five lumbar, five sacral, and four coccygeal. In the adult state it forms a double sigmoid curve, caused, in the dorsal and sacral regions, by the conformation of the vertebræ–in the cervical and lumbar regions, by the elasticity of the ligamenta subflava connecting the posterior arches. In the skull, the occipital condyles are placed, if not exactly in the centre, within the middle fifth of the base, being slightly behind the centre in the lower races. The mastoid processes are largely developed. The cranio-facial angle in well-formed skulls is about 90°, and probably never exceeds 120°. In consequence of the enormous size of the cerebral cavity, the length of the head is always more than twice the length of the basi-cranial axis.^a In the interior of the skull the ethnoid and presphenoid meet in the floor of the cavity, and are not concealed by the frontal; the inner surface of the petrosal has no fossa for the lodgment of a process of the cerebellum; and the planes of the occipital foramen, cribriform plate, and tentorium are parallel to one another. The hyoid bone is comparatively narrow from above downwards, and, though concave posteriorly, not deeply excavated. In the limbs the pectoral arch has a well-developed clavicle, and a large and broad scapula; the humerus has a large globular head, and at the lower end a rounded facet upon which the radius plays, allowing free pronation and supination. The form of the pelvis is eminently distinctive–the breadth and curvature of the sacrum, the great extent and concavity of the inner surface of the iliac bones, the sigmoid flexures of their upper margin, the mode in which the pelvis is set on the spinal column, the breadth of the upper aperture, and the width and shortness of the whole cavity, may specially [155] be noted. In the lower extremity may be observed the great angle at which the head of the femur is set on its shaft, the greater length of the internal than the external condyle, the flatness of the upper surface of the tibia, the form of the ankle-joint, and the downward projection of the malleoli.

To sum up the peculiarities of the human skeleton, we find that its special characteristics, as distinguished from those of the general Mammalian type, have all (leaving aside the upper extremity) reference to the erect posture. To this end contribute the form of the ankle-joint, of the upper surface of the tibia, of the condyles and head of the femur, and of the pelvis; the curvatures of different parts of the spinal column, the position of the ribs, the breadth and flatness of the sternum, and the situation of the occipital condyles. Moreover, related to the same posture are the absence of great bony crests on the skull for the attachment of the muscles which support the head in the lower animals, the smallness of the jaws and teeth, and even the great mass of the brain, which would be of little avail unless the anterior pair of limbs had been set free to carry out its requirements.

(a) These terms are explained in the last Course of Lectures. See Medical Times and Gazette, 1863, vol. i., p. 607.

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Professor Huxley's second lecture was devoted to an account of the structure of the bones and muscles of the human hand and foot. The skeleton of the hand is divided, he said, into three regions, the carpus, metacarpus, and digits. The carpal bones are disposed of in two rows, four in each, although the pisiform of the first row can hardly be looked upon as belonging to the group, but is rather a sesamoid bone of a muscle. The whole of the bones of the hand may be divided into two sets, a tridigital radial series, including the scaphoid, lunar, trapezoid, trapezium, magnum, and three first digits, and a bidigital ulnar series, including the cuneiform, unciform, and fourth and fifth digits. When the hand is viewed on its dorsal or palmar surface, a line drawn across the articulations of the four outer metacarpal bones with the carpus forms an obtuse angle with a line drawn in the plane of the carpo-metacarpal articulation of the pollex; this was characterised as the "digital angulation." When the distal articular surfaces of the lower series of the carpal bones are looked at, it will be seen that in this direction also the surface of the trapezium to which the metacarpal bone of the of the thumb articulates, forms an angle, which may be termed the "palmar angulation." It is to the direction and form of this articular facet that the thumb of man owes its peculiar opposability.

The movements of the different joints of the terminal divisions of the hand are flexion and extension in every case; at the metacarpo-phalangeal articulation alone, another motion, that of circumduction, is allowed, consequent upon the roundness of the head of the metacarpal bone. The muscles of the fingers may be grouped as flexors, extensors, and divaricators, the last pulling the digit out of the straight direction to one or the other side. The index-finger has nine muscles; three extensors–the extensor carpi radialis longior, inserted into the base of the metacarpal bone; the extensor communis digitorum; and the extensor indicis, the tendons of which unite, and are then inserted by two slips into the bases of the first and second phalanges. The flexors are also three–the flexor carpi radialis, inserted into the metacarpal bone and the flexor sublimis or perforatus, and flexor profundus or perforans, inserted into the second and ungual phalanges respectively. The divaricators, or "flexor-extensors" as they might be called are the two interossei and the lumbricalis. The action of these muscles is very important in producing the varied movements of the fingers. The interosseous muscle of the index-finger, situated to the radial side, belongs to the group called "dorsal;" the one on the other side is said to be "palmar." This distinction only refers to their mode of origin from the metacarpal bones, and is unimportant, as at their extremities they are on the same level, and they are inserted in precisely the same mode, viz., each divides into two tendons, one of which is inserted into the side of the base of the proximal phalanx; the other, more slender, passes upwards and backwards, and joining its fellow from the opposite side, is inserted into the posterior surface of the base of the distal phalanx, of which it is the proper extensor; thus, the two interossei of any given finger acting together, are flexors of the proximal, and extensors of the distal phalanx. This was pointed out and proved experimentally by Duchenne, in his work, "De l'Electrisation Localisée." One of the muscles acting separately, is a divaricator of the finger into which it is inserted. The lumbricales are also, to a certain extent, divaricators, and are flexors of the second, and extensors of the distal phalanges.

The number and nature of the muscles differ in every finger. The third digit has seven; the fourth only six–the extensor and flexor of the metacarpal bone, and the extensor proprius, found in the index, being absent. The fifth is the most abundantly supplied with muscles, having eleven in all,–three flexors, three extensors, three divaricators, and two special muscles, the flexor brevis, and opponens. The thumb has nine muscles, but very differently disposed from those of the index finger. There are three direct extensors (of one of these, the extensor ossis metacarpi pollicis, it may be noted that it sends a slip of insertion to the trapezium); there is but one long flexor; two divaricators, the abductor, and a small muscle unnoticed in English works, but described by Henle as "interosseus palmaris primus," arising from the trapezium and base of the metacarpal bone, and inserted into the extensor sheath; there is no lumbricalis; the special muscles are, flexor brevis, opponens, and adductor. Connected with the last-named muscle, there is often a fleshy bundle, having a tendinous origin from the head of the fourth and fifth metacarpal bones, which might be called "transversus manus." It is further to be noted in the hand, that all the direct extensors and flexors are long muscles, that is, they arise from the bones of the arm; and that there is no muscle coming from the ulnar side, with a tendon crossing the palm and inserted into the first metacarpal bone, like the peroneus longus in the foot.

In the foot, the tarsal bones are seven in number, but not clearly divisible into a proximal and distal series. Like the hand, the whole skeleton of the foot can be arranged in a tridigital inner division, including the astragalus, navicular, and three cuneiform bones, and a bidigital outer division, containing the calcaneum and cuboid. The digital and plantar angles formed by the articular surface of the first metacarpal bone with those of the other four, is nearly as well marked as in the hand; but, in consequence of the axis of the metatarsal bones not being perpendicular to their articular facets, as in the metacarpals of the hand, the hallux is parallel to the other digits. The articular facet for the first metatarsal, on the entocuneiform bone, is nearly flat, having none of the peculiar saddle-shape of the corresponding surface in the hand. It is in consequence of this conformation of the bones, and not from the want of special muscles, that the hallux is unable to execute the motions of the pollex in man, and that the great apparent difference of the foot and hand arises.

The second, third, and fourth digits have each seven muscles, two direct extensors, long and short, two direct flexors, perforated and perforating, and three divaricators, the two inter[178]ossei and lumbricalis, all having the same insertion as in the hand. The fifth toe has ten muscles, including the peroneus tertius as an extensor, and the peroneus brevis as a flexor of the metacarpal bone; a flexor brevis and an opponens, the last a distinct muscle inserted into the whole length of the metarsal bone, though commonly ignored in anatomical works. The hallux has ten muscles, three direct extensors, including the tibialis anticus, which is inserted by a distinct tendinous slip into the base of the first metatarsal bone, as well as into the entocuneiform bone; one direct flexor; two divaricators, the abductor, and an inconstant "interosseus palmaris primus," and four special muscles,–the flexor brevis, abductor, transversus pedis (often rudimentary), and the peroneus longus. The hallux is thus provided with more powerful muscles for opposition than the pollex; but, in consequence of the fixity of the bone into which it is inserted, the function of the last-named muscle is not to adduct the toe, but to steady the leg in the upright position.

There remain yet to be particularly described the great flexors of the toes, the flexor digitorum longus or perforans, the flexor brevis or perforatus, the flexor hallucis longus, and the flexor accessorius. The arrangement of these in the sole of the foot is very complex, and varies so much that it is rare to find it perfectly alike in any two individuals; and, moreover, the descriptions given in the text-books of anatomy are altogether incorrect. Professor Huxley stated, as the result of his own dissections, that the tendon of flexor hallucis generally divides into two slips, one for the first digit, and the other, of varying size, passing to the two or three succeeding digits, and uniting with slips from the tendon of the flexor longus digitorum and the accessorius, but that it had never been observed to furnish any part of the tendon of the fifth digit. The details of these arrangements in several individual cases were described, illustrated by preparations and drawings.

[203]

Professor Huxley commenced by quoting a statement of Vic d'Azyr to the effect that, besides the comparative anatomy which aims at comparing the same parts in different animals, there is another comparative anatomy, which has for its object the comparison of the resemblances and differences between corresponding parts of the same individual. Last year, Professor Huxley stated, he had taken up one part of this great subject, and instituted an examination of the skull and vertebral column, with a view to ascertain how far they were constructed upon the same plan, the result having been that the supposed resemblance did not exist; it was, however, otherwise with the anterior and posterior extremities, which as is universally admitted, present a remarkable accordance throughout their construction. To point out the details of this accordance is by no means an easy problem, and consequently has received many different solutions. None of these, not even the one now proposed, can be considered as thoroughly satisfactory, as they have not been checked by the aid of a complete study of the development of the parts in question, the only method by which any morphological problem can be absolutely determined. Vic d'Azyr, who took up this subject in the latter part of the last century, thought that the comparison could only be carried out by taking the anterior and posterior limbs of opposite sides, the right upper with the left lower, and vice versâ, a theory which has met with little or no support. Bourgery and Cruvielhier, seeing that the thumb corresponded with the great toe, and the lower ends of the radius and ulna with those of the tibia and fibula respectively, thought that it was the reverse with the upper ends of these bones, a crossing taking place in the middle of the forearm. Flourens and Martins accounted for the difficulty of the different direction of the articular surfaces of the femur and humerus by supposing that, while the former was a straight and unmodified bone, the latter was twisted on itself to the extent of 180° in man and the higher mammals.

Regarding these theories, and some minor ones which were alluded to, as more or less untenable, Professor Huxley instituted a new comparison of the limbs, placed, not in the position which they assume in adult life, but in the only one in which they really correspond with each other, viz., that which they first exhibit in the embryo. In this condition they stand out at right angles from the body, the extensor surface being placed dorsally, and the flexor surface ventrally, the same for both pair of limbs. They then gradually become bent, and afterwards acquire the modified position which suits them for their functions in life, and to which the various articulations become adapted. The embryonic position continues through[204]out life in many Amphibia and Reptiles, and without much change in Galeopithecus among Mammals.

The special homotypes of the bones of the extremities were then shown; the division of the bones of the hand and foot into the previously-mentioned tridigital and bidigital series, greatly aiding the comparison. The correspondence of the pollex and hallux and of the other digits, has been admitted by everyone. The unciform, magnum, trapezoid, and trapezium of the hand correspond very well with the cuboid and the cuneiform bones of the foot. About the remaining bones there is more difficulty; but there can be little doubt but that the cuneiform and pisiform of the hand correspond to the calcaneum, the lunar to the astragalus and the scaphoid, together with the ninth bone which appears in the carpus of most Apes and many inferior Mammals, to the navicular. The radius was then shown to be homotypical with the tibia, and the ulna with the fibula, all having, however, undergone remarkable adaptive changes in their upper extremities, the ulna being enlarged in this part in the arm, and the tibia in the leg. The correspondences of the humerus and femur were then pointed out, and especially the change that their articular heads have undergone in direction in accordance with the requirements of the positions of the body; and it was shown that, owing to the alterations from the original position of the limbs, the fore-part of the arm corresponds morphologically with the hind part of the leg, and the outside of the one with the inside of the other.

The pectoral and pelvic arch offer, at first sight, some difficulties, but by no means of an insuperable nature. The scapula can readily be shown to correspond to the iliac bone, its upper border to the "linea arcuata interna," forming the brim of the pelvis, the spine and acromion to the upper portion of the ilium, the supra-spinous fossa to the iliac fossa. A comparison of the scapula and ilium of the Ornithorhynchus shows this relation very clearly. It is generally considered that the pubis and clavicle are homotypes, but there are several strong objections to this view; the attachment of the muscles and the relation of the great vessels are entirely different in each, and what is more important, the pubis is developed in a pre-existing cartilage, which the clavicle is not. That which corresponds to the clavicle in the lower limb appears to be Poupart's ligament, which, if ossified, would agree well with it in the attachment of muscles and relations of the large vessels and nerves. The coracoid represents the pubis, or the pubis and the ischium, in Man and the higher Mammalia. This resemblance is strengthened by the fact, that in monotremes and reptiles there are two coracoids, with occasionally an aperture between them corresponding to the obturator foramen of the pelvis.

The correspondence that may be traced between the muscles of the anterior and posterior extremities, although not so exact as that existing between the bones, is so well marked that it cannot be regarded as accidental. Many of these have been already alluded to in the preceding lecture, as the mode of insertion of the extensor and the perforating and perforated flexor tendons into the phalanges. The following are the principal muscles of the leg, which clearly correspond to others in the hand:–The tibialis anticus, with its double insertion into the entocuneiform and base of first metatarsal bone to the extensor ossis metacarpi pollicis, inserted into the trapezium and the base of the first metacarpal bone; the difference between them being, that in the first case the larger insertion is into the proximal bone–in the latter, into the distal bone. The peroneus brevis with the gastromenius and soleus, correspond with the extensor carpi ulnaris, being functionally enlarged in the lower extremity; the tibialis posticus with the flexor carpi radialis; the flexor longus digitorum of the foot with the flexor digitorum profundus of the hand; the flexor brevis digitorum of the foot with the flexor digitorum sublimis of the hand; the extensor longus digitorum of the foot with the extensor communis of the hand; the popliteus with the pronator teres; the gracilis and sartorius with the biceps flexor cubiti; the great adductors with the coraco-brachialis; the iliacus with the supraspinatus; the glutei with the infra-spinatus and teres, etc.

Among the principal differences between the muscular arrangements of the two extremities may be noticed the absence of an opponens to the first metatarsal bone of the foot; this seems an important character, as it is pretty constant in the lower groups of Mammalia. There is a slight difference in the origin of the interossei in the space between the second and third metacarpal and the corresponding metatarsal bones, but without any alteration of their function. In the front limb there is no flexor or extensor arising in the hand, and in the posterior limb there is no flexor or extensor arising from the femur. In the arm the long flexors of the thumb and other digits each arise on the same side of the limb as that to which they are finally distributed. In the leg they arise from opposite sides, and their tendons cross each other. In the hand there is no interweaving of these tendons together, as in the foot. In the hand there is no muscle corresponding to the flexor accessorius. In the arm the extensor muscles cross each other, but in the leg they do not. The quadriceps extensor muscle of the leg has generally been supposed to correspond with the triceps of the arm, but this can scarcely be the case,–the former is situated both in its origin and insertion on the tibial side of the limb, the latter, on the ulnar side; so, though agreeing in function, they differ in homological structure. After leaving the bones and muscles, it becomes a very difficult matter to trace the homotypes among the nerves and vessels, and one which can only be made out by a careful study of development.

[229]

The structure of the brain deserves a most careful consideration in connexion with the subject of the present course of lectures, as many of the characters of the groups of the Mammalia have been based upon it. The form of the brain can only be studied upon specimens hardened in situ, or from casts of the interior of the cranial cavity, as it immediately loses its shape and the relative situation of its component parts on removal from the body. A series of casts of the cranial cavity of different races of men and various animals have lately been added to the College Museum. Foremost among the morphological characters of the human brain may be given its great relative size; though its form varies much, as a general rule the cerebrum is highest in the parietal region; it covers and projects beyond the cerebellum posteriorly, and it covers and projects beyond the olfactory lobes anteriorly; it has a very slight supra-orbital excavation, which is in relation to the slight projection of the roof of the orbits into the cavity of the skull, and the supra-cerebellar excavation is not deep.

The entire encephalon is capable of division into three principal parts:–1. The fore-brain, consisting of the olfactory lobes, the cerebral hemispheres, and parts surrounding the third ventricle; 2. The mid-brain, the corpora-quadigemina, and the crura-cerebri; 3. The hind-brain, the cerebellum, pons Varolii, and medulla oblongata. Of these the first and last are further divisible into segments. The segments of the fore-brain may be called–1. Olfactory; 2. Hemispheral; 3. Thalamary. Those of the hind brain are–1. Cerebellar; 2. Oblongate. The mid-brain does not need further subdivision.

The olfactory segment in man is extremely small, and has no internal cavity. The characters of the large and important hemispheral segment requires very careful study; each hemisphere is generally divided into three lobes, but the boundaries of these are very vague. A better division is that of Gratiolet, whose work on the "Cerebral Convolutions of Man and the Primates" is the best that has been written on the subject. He divides the external surface of the hemisphere into five lobes, which are called–1. Frontal; 2. Parietal; 3. Temporal; 4. Occipital, and 5. Central; the last is the "island of Reil," placed at the bottom of the fissure of Sylvius. The surface of the hemispheres is covered with a labyrinth of elevations and fissures–gyri and sulci , as they are technically called. Although at first sight looking most confused, careful attention will detect order, and they can be without difficulty arranged and named, as has been done by Gratiolet, in the following way:–In the first place there are certain fundamental sulci; of these the most important is the well-known fissure of Sylvius. In front of this, on the upper and lateral part of the brain, is a deep, well-marked, and exceedingly constant transverse sulcus, called the fissure of Rolando; this is bounded both in front and behind by two large convolutions, which run nearly transversely, passing slightly backwards at their upper end; these are the antero-parietal and postero-parietal gyri. With the exception of these two, all the gyri of the outer side of the hemisphere, run more or less in the longitudinal direction. They are easily remembered–being three on each lobe, and placed in tiers one above the other. On the frontal lobe are the infero-frontal, medio-frontal, and the supero-frontal; on the temporal lobe, the antero-temporal, medio-temporal, and postero-temporal; on the occipital lobe, the infero-occipital, medio-occipital, and super-occipital. Bounding the upper extremity of the Sylvian fissure is an arched convolution called the angular gyrus; and connecting the postero-parietal, angular, and temporal gyri with the occipital are a series of small convolutions called the annectent gyri; they usually bridge over a fissure which occasionally exists, called the external perpendicular sulcus.

Upon the inner surface of the hemisphere, or that which is turned towards its fellow, are certain well-marked and important fissures. Between the upper surface of the corpus callosum and the margin of the hemisphere is one running in the longitudinal direction, the calloso-marginal. On the posterior part is a deep and constant fissure, also longitudinal, called the calcarine; and above this, and placed more vertically, the internal perpendicular. Below the calcarine, and running down towards the bottom of the temporal lobe, is the collateral sulcus; and close to the posterior margin of the ventricular aperture is a deep sulcus, the dentate, containing within it a small convolution commonly called the "fascia dentata." The principal gyri on the inner side of the hemisphere are the callosal, marginal, uncinate, and the quadrate lobule. Certain of these external markings have very definite relations to internal portions of the cerebrum.

Each hemisphere has within it a great cavity–the lateral ventricle–which has prolongations, or cornua, extending in three different directions, anterior, middle, and posterior. The whole cavity has a remarkable relation to the corpus striatum, being, as it were, curled round it; so that this body forms the floor of the middle part of the ventricle, but the roof of its posterior and outer portion. The corpus striatum, in fact, is an outward growth from the middle of the base of the hemisphere, and forms the axis around which the whole is developed. It is also in close relation externally with the central lobe, anteriorly and below with the substantia perforata antica, and internally with a smooth space below the beak of the corpus callosum, which might be called the "substantia lævis." In the descending corner of the lateral ventricle is an elevation corresponding to the dentate sulcus, called the hippocampus major; in the posterior corner is the hippocampus minor, or calcar avis, corresponding with the calcarine sulcus; and between the two is placed the eminentia collateralis, or pes accessorius, corresponding to the collateral sulcus.

[256]

In this Lecture the description of the structure of the human brain was continued. On the inner surface of the cerebral hemisphere is an aperture leading from the third ventricle into the cavity within the hemisphere; this is the foramen of Monro. The aperture is prolonged backwards as a cleft (in the undisturbed condition of the parts closed by membranes), which constitutes the lateral portion of the so-called "great transverse fissure of the brain." The lower boundary of this cleft is a thin white band called the tænia semicircularis. Above and in front of the opening is a portion of the inner wall of the hemisphere, closing the lateral ventricle towards the middle line, which may be called the "septal area." The free, inferior margin of this area, which is thickened, constitutes the body and posterior crus of the fornix. Besides the anterior pillars of the fornix (small white bands passing down to the corpora albicantia, behind the anterior commissure),there are numerous longitudinal fibres passing forwards from the fornix in the septal area, above and in front of the anterior commissure; these may be called the "pre-commissural" fibres; they are less developed in Man than in the lower Mammals. The upper part of the septal area is very thin, constituting the "septum lucidum," which may also be described as the part of the inner wall of the hemisphere situated immediately above the anterior part of the fornix and the pre-commissural fibres. The corpus callosum is a great mass of transverse fibres, running from the inner wall of one hemisphere to that of the other, above the longitudinal fibres of the septal area, and forming the roof of the inter-hemispherical cavity or fifth ventricle, and also on each side the roof of the lateral ventricles. In Man this great transverse commissure is exceedingly large; it reaches back so far as to cover the corpus quadrigemina, and almost to touch the cerebellum. Its hinder part is called the splenium, and is very much thickened, containing commissural fibres, not only of the part of the hemisphere immediately opposite to it, but those from all the posterior portions; the middle part, of great length in Man, is the proper corpus; the front part makes a strong bend, the genu; the part that is reflected underneath being called the rostrum. From the latter a delicate layer, the rostral lamina, passes to the upper part of the anterior commissure, though it is doubtful whether it consists of true cerebral matter.

The principal characteristics of the cerebral hemispheres of Man are, their vast size in proportion to the other parts of the encephalon and to the nerves which arise from them; the large size of the frontal lobe, the sulcus which separates this region from the parietal being situated far back; the charac[257]teristic form of the central lobe or insula, somewhat V shaped, and divided vertically by a deep fissure, each half further sub-divided by radiating sulci into a number of folds; the great development of the annectent gyri, which usually leads to the entire obliteration of the external perpendicular fissure, and to the extreme reduction of the occipital lobe; and the great obliquity of the fissure of Sylvius. On the internal surface of the hemisphere may specially be noted in the human brain, the obliquity of the internal perpendicular fissure, the downward direction of the hinder part of the calcarine fissure, the proportionate smallness of the uncinate gyrus, the thinness of the septal region, and the great size of the corpus callosum, particularly the large development of the genu, rostrum and rostral lamina.

The thalamary segment of the brain is formed by the optic thalamus on each side, prolonged below into the infundibulum and pituitary body. Its roof is formed by the velum interpositum. The anterior boundary is an almost perpendicular wall, passing down from the anterior commissure to the optic commissure, called the lamina terminalis. The optic commissure itself forms part of the inferior and anterior boundary of the third ventricle, which is the cavity of this segment. The anterior descending pillars of the fornix also belong to the thalamary segment. The mid-brain consists above of the corpora quadrigemina, below of the crura cerebri; the "iter a tertio ad quartum ventriculum" is its ventricle. In the hind brain, the great development and anterior convexity of the pons, and absence of corpora trapezoidea are characteristic of Man, as is also the small size of the flocculus and of the vermis, as compared with the lateral parts of the cerebellum.

A sketch of the modifications which the human brain undergoes during its development will render intelligible, and afford useful material for comparison with, many of the permanent conditions of this organ in the lower vertebrates. In its earliest condition, the embryo has, on its upper surface, a groove, called the "primitive groove." This becomes widened in front; and from this part the future brain commences, in a cellular substance, originally in strict continuity with the epidermal layer of the embryo. In the anterior widened portion of the groove, three dilatations take place, one behind the other. The lips of the groove growing up unite in the middle line; so that a tube is formed with three vesiculations–anterior, middle, and posterior–corresponding with the three primary divisions of the brain before given. In the course of development, a bending of the whole takes place, the middle vesicle being at the top of the bend. From the sides of the anterior vesicle, grow out two hollow bags, which rapidly enlarge and eventually become the cerebral hemispheres. From the front of these, another prolongation, at first also hollow, forms the olfactory segment; while the remaining part of the primitive anterior vesicle becomes the thalamary segment. The growth of the hemispheres so far transcends that of the other segments, that they soon cover them all; and at the fifth and sixth month actually project further beyond the cerebellum than they do in a later period of life. From the floor of the great cavity in the hemisphere, the corpus striatum grows up, and forms an axis, around which the white hemisphere becomes curved; so that what was at first the hinder becomes the lowermost part. On the inner surface, the original aperture of communication with the primitive segment, from which the hemisphere is an offshoot, becomes the foramen of Monro; from the upper border of the aperture, the fornix is formed; and from its inferior border, the tænia semicircularis. On the hemispheral side of the latter, grows up the corpus striatum; on the other side, the optic thalamus. On the external surface of the hemisphere, a space is formed corresponding to the outer surface of the corpus striatum. This is the future central lobe, or island of Reil, at first perfectly smooth and uncovered, and only at an advanced period of inter-uterine life concealed by the lips of the Sylvian fissure. The temporal lobe is developed at an early age; but the occipital lobe is a subsequent outgrowth from the hinder part of the hemisphere. At first, the surface is perfectly smooth; at about the sixth month, sulci appear. The earliest of them that can be distinctly recognised are the antero-parietal on the outer surface, and the calloso-marginal calcarine, and internal perpendicular on the inner face.

The development of the corpus callosum is a subject of considerable difficulty. According to Reichert and other trustworthy observers, at one time the hemispheres are perfectly unconnected, except by the lamina terminalis of the third ventricle. Upon the inner wall of the hemisphere is a thin depressed area, corresponding with what has been described above as the septal area; from out of the substance of the wall at the upper margin of this space transverse fibres grow out, and unite with corresponding fibres from the opposite side, thus forming the commencement of the future great commissure. Certain changes in the walls of the third ventricle only require to be noticed; by differentiation of part of its anterior boundary, a band of transverse fibres passing between the corpus striata is formed; this is the anterior commissure. Behind this, longitudinal white cords grow up from the optic thalamus and unite with the fornix, of which they form the anterior pillars; and, lastly, the upper portion of the vesicle becomes metamorphosed into the vascular "tela choroidea," which closes in the ventricle above.

[284]

The form, arrangement, and mode of succession of the teeth constitutes an important subject of study in connexion with the structure and classification of the mammalia. The teeth of man are composed of the ordinary constituents, cementum, dentine, and enamel, are fixed in alveolar sockets, and consist of a temporary and permanent set, the latter replacing the former vertically. In both jaws the range of teeth form an arch, with the horizontal surface very nearly level, but the planes of the grinding surfaces of the upper molars look, slightly outwards, the reverse being the case with the lower ones, so that the inner edge of the upper series and the outer edge of the lower series become worn first. The upper incisors bite in front of the lower ones, and the direction of the axis of the lower canine is slightly in advance of that of the upper. The line of the teeth is unbroken by any such intervals as usually occur in the lower animals.

The teeth are divided, for convenience of description, into incisors, canines, premolars, and molars. The incisors are defined–at least, as regards those of the upper series–as those teeth which are lodged in the premaxillary bone. The suture which limits this bone is soon obliterated in man, but traces of it can often be seen on the palatal surface. The tooth situated immediately behind the premaxillary suture is called the canine, but there is no absolute mode of distinction between it and the succeeding teeth, or premolars. The peculiar form and size is the general test adopted, but this fails in the examination of the dentition of some animals. The molars are distinguished from the canines and premolars by their mode of development; they do not succeed any other teeth vertically as these do.

The special characters of the human teeth are the following:–In the upper jaw the incisors are two on each side, single-fanged, adze-shaped, narrow from before backwards, and with broad, cutting edges; the outer are smaller than the inner pair. The canines are obtusely pointed, wedge-shaped in section, not larger than the inner incisors, with a stout, long fang, which causes a marked projection on the outer surface of the maxilla. The premolars, two on each side, are much like each other, have an elliptical transverse section, fang single or more or less divided, crown with two cusps, outer and inner, of about equal size, though the outer projects somewhat beyond the level of the other. The true molars are three in number; the two anterior of nearly equal size, and the posterior smaller. Their crowns are of quadrate form, with a peculiar pattern on the surface, composed of four projections or cusps at the corners, with a depression between them crossed diagonally by a ridge which connects the anterior internal with the posterior external cusp. This pattern is [285] less definitely developed on the posterior molar. In the lower jaw the number of each class of tooth are the same as in the upper. The discrepancy of size in the incisors is not so great, and the inner one is the smaller of the two. The canine is not so large as in the upper jaw. The crowns of the premolars are more nearly circular, the inner cusp is considerably smaller than the outer, and generally connected with it by a transverse ridge. The three lower molars have somewhat larger crowns than the upper ones, and have a different pattern on their grinding surface, being divided by a conical groove into four cusps, with an additional small tubercle behind the posterior external cusp.

A representation of the number of the different kinds of teeth in both jaws by means of symbols constitutes what is called a "dental formula." The number and nature of the permanent teeth of man are thus shown by the convenient signs put forward by Professor Owen:–

It will thus be seen that this set, or the "milk" teeth as they are sometimes called, differ considerably in number from those that replace them. They differ also in their characters. In the upper jaw the crown of the first deciduous molar is considerably smaller than that of the second, and is bicuspid. The posterior one has the pattern of a true molar, and is, therefore, more complex than the tooth which succeeds it. The same rule holds with the lower deciduous molars, the first more resembling a bicuspid, and the second a true quinquecuspid molar. As to the order of succession of the teeth in man, the principal point to be noted, in reference to zoology, is that the canine comes into place in each of the jaws before the second molar.

Professor Huxley next proceeded to give an account of the organs and processes of reproduction in man. In the male the penis is external, pendulous, and not fastened by a preputial sheath to the abdomen; the testes are suspended in a well-developed scrotum, and the canal of communication between the abdominal cavity and the tunica vaginalis is completely closed in the adult. The urethra is divisible into–1. An anterior portion contained in the corpus spongiosum, and into which the ducts of Cowper's glands open; 2. A middle or membranous portion; 3. A prostatic portion, which receives the ducts of the prostate gland, the vasa deferentia from the testes, the sacculus prostaticus, a small and apparently insignificant sac, varying much in dimensions, and, lastly, the cystic portion of the urethra, or proper urinary canal, extending from the neck of the bladder to the anterior part of the verumontanum.

It is not difficult to identify certain portions of the male reproductive apparatus as corresponding with some of the female organs: thus the testis and ovary represent each other in the different sexes; the scrotum answers to the labia majora; the glans, prepuce, and cavernous bodies of the penis to the similar parts of the clitoris; Cowper's glands to Bartholin's glands; and the prostatic sac to the vagina and uterus. The prostate is not at all represented in the female, as far as we know at present.

When this problem is prosecuted further by the aid of the study of development, it presents one of the most remarkable instances of unity of plan, with diversity of modification, in the whole animal kingdom. At one period of its existence, the vertebrate embryo appears, at all events structurally, absolutely sexless. The rectum and bladder and reproductive ducts terminate in a common chamber which opens externally. There are two ducts on each side; the inner one connected above with the Wolffian body, the primordial functional kidney. The outer, or Müllerian, duct is a blind canal, connected above with no gland or other organ. Behind the Wolffian body, the true kidney with its duct developes; in front of it arises another body, which ultimately becomes testis or ovary, as the case may be. In the male, the last named body gradually acquires the tubular structure of the testis; and the Wolffian body, losing its function as a kidney, becomes converted into the epididymis and coni vasculosi, and its duct becomes the vas deferens. The Müllerian duct remains without function, and is in great part obliterated; its upper part becoming the inconstant vas aberrans, and the coalescence of the inferior extremities of the two forming the prostatic sacculus. In the female, on the other hand, it is in the Müllerian ducts that the greatest amount of development takes place: their upper extremities become the Fallopian tubes; their lower parts fused together form the uterus and vagina. The Wolffian body becomes the quite insignificant parovarium, the lower part being completely obliterated. These transitory conditions of the reproductive organs of the human fœtus are of great interest, as some of them remain more or less permanent among the lower Mammalia.

[312]

This lecture was devoted to a survey of the development of man, from the ovum up to the adult condition. The formation of the Graafian follicles, and the process of "ovulation," or emission of an ovum, was first described. This process occurring at regular intervals gives rise to a remarkable disturbance in the economy, one of the principal effects of which is a determination of blood to the uterine parietes, proceeding to the extent of causing actual rupture of the vessels of the mucous membrane, with escape of a portion of blood into the cavity of the uterus, which being mixed with the uterine secretions and epithelium, constitutes the menstrual fluid. Should no impregnation occur, the ovum passes away, and the uterus and ovary return to their previous condition; but if the ovum should become impregnated by contact with the spermatic element of the male, a remarkable series of changes take place in the ovary, uterus, and in the ovum itself.

The changes in the ovum, and the early stages of the formation of the embryo, with its amnion, chorion, and allantois, are well known. In the ovary the corpus luteum is formed by a large quantity of exudative matter thrown out around the outer surface of the Graafian follicle. The walls of the uterus become extremely vascular; the capillaries acquire a great size, adapting their calibre to the increased pressure upon them by a process of growth, so that there is no rupture as in the temporary congestion of the menstrual period; the muscular fibres increase in number and length; the [313] nerves increase, and more than any other part, the mucous membrane with its numerous cæcal follicular glands. Around the spot at which the ovum is lodged a fold of mucous membrane grows up, and still containing glands and vessels surrounds the whole ovum. The rapid growth of the latter, however, distends it greatly, and causes it to lose part of its original structure. This constitutes the so-called "decidua reflexa," the part of the mucous membrane between the ovum and the uterine wall forms the "decidua serotina," and the remaining part upon the inner surface of the cavity the "decidua vera." By the middle of pregnancy the latter loses its vascular connection with the tissues below, can readily be stripped off, and a new growth of lining membrane takes place beneath it.

The villi of the chorion, at first scattered all over the surface, afterwards become limited to a particular region, opposite to the decidua serotina; and the interaction of these two structures leads to the formation of the placenta. The glandular parts of the mucous membrane become obliterated by the enormous development of the intervening blood-vessels, which assume the form of large sinuses; into these sinuses the greatly-developed villi of the fœtal membrane project, so as to allow of an interchange of materials between the blood circulating in the mother and the embryo.

The human ovum is thus, at first, implacental, then villi are formed on the chorion, but not attached to the maternal mucous membrane; it is placentate, but not deciduate. Lastly, the villi and the mucous membrane become so closely attached that they cannot be separated without injury. After the separation of the placenta in the process of parturition, it is found to contain, not only parts belonging to the fœtus, but also maternal structures, the walls of the venous sinuses developed in the original mucous membrane of the uterus forming its outer portion. The changes in the uterus subsequent to birth consist in regeneration of the mucous membrane over the space from which the placenta was removed, and assumption of the usual condition of all the tissues of the organ by a process of retrogressive metamorphosis.

Among the changes which the fœtus undergoes in its development, some of the most interesting (especially in relation to zoology) are those affecting the form and proportions of the body. In a fœtus an inch and a-half long from the vertex to the heel, the head is from one-third to one-fourth of the entire length; the arms are not so long as the spine, and are about the same length as the legs. The forearm is about the same length as the upper arm, and the leg is about equal to the thigh. The hands and feet are very much alike, and the thumb and great toe are not so different from the remaining digits as at a later period. In a fœtus four inches long, the head is one-fourth of the entire length; the arms are longer than the spine by one-sixth of their length, and are a little longer than the leg. In a fœtus eight inches long, the head is less than one-fourth of the whole length; the arms are longer than the legs, so that the extremity of the fingers reach down to the knee; the forearm is longer than the upper arm, and the thigh than the leg. At term the head is less than one-fourth of the whole length, the legs longer than the arms, the upper arm longer than the forearm, and the thigh than the leg. The hands and feet are about equal. It is thus seen that the proportions of the body change during intra-uterine life by a law of growth which does not act uniformly throughout the whole period,–the head regularly diminishes in proportion to the rest of the body, but the arms grow proportionally quicker at the middle, and the legs at later portion of the period. After the middle of gestation, also, the proximal segments of the limbs take on a more rapid development than the middle segments.

After birth changes of proportion continue to take place in the same direction as those which have occurred in the later portion of intra-uterine life. These changes were illustrated in the lecture by a series of diagrams, copied from the work of Liharzik, and may be summed up as follows:–The entire length of the adult has increased, on an average, to three and a-half times the length of the new-born infant. The head increases at a comparatively small rate, being in the adult only twice the size in the infant. The proportion of the arms to that of the other parts remains constant, the rule that the distance from tip to tip of the outstretched fingers equals the height being good for all ages. The legs gradually increase in length, as compared with the body; at the birth the central point between the vertex and sole is situated at the umbilicus, in the adult a little below the symphysis pubis. While the arms of the adult are but three and a half times the length of those of the infant, the legs have increased to five times the length.

Although, even at birth, some differences independent of proper sexual characteristics are perceptible between the sexes–the female infant being, as a rule, slightly smaller than the male–it is only as maturity approaches that the special distinctions of form and proportion are developed. The chief of these are the following:–The female is smaller than the male, the disproportion between them being greater in the tall than in the short race of men; the female head is proportionately somewhat larger than the male; the thorax, and especially the sternum, is shorter in the female, and the abdomen is longer; the legs are a little shorter, and the female pelvis, as is well known, is absolutely broader and of different form from the male. In all these differences, except the last-named (which is directly connected with the reproductive function), the female retains more of the infantile characteristics than the male. A parallel observation has been made upon the intellectual capacity of the sexes.

[343]

The variations in the form and proportions of the human body, under the different circumstances which have given rise to the various races of man upon the earth is an interesting and fertile subject for study, but one which has hitherto been cultivated to a very small extent with anything like the precision which its importance demands. All human beings naturally assume the erect posture, and all agree in certain great and fundamental characters in respect to the proportions of the body; thus, the legs are always longer than the arms, the tips of the fingers do not reach the knees in the upright position, the proximal segments of the limbs are the largest, the foot is longer than the hand, the hallux never greatly shorter than the second toe, and can never be greatly abducted or opposed. There are, however, both in individuals and races, considerable minor variations of proportions, the chief of which will now come under consideration.

From a series of measurements of skeletons of Europeans and negroes, published by Dr. Humphry, it appears that the average height of the negro is less than that of the European, the arms are proportionally longer, particularly the forearm and hand; and in the lower extremity, while the femur retains nearly the same relative length as in the European, the tibia and foot are considerably increased. In these deviations from the European standard, the Australian and other low races agree with the negro; and it will be observed they recall some of the peculiarities of the proportions of the fœtus, and will be met with, only in an infinitely more marked degree, in some of the anthropoid mammalia. There is no real evidence to show that the hallux is differently constructed, or more moveable, among the lower than in the higher races of men, though in the latter the practice of wearing hard shoes rarely allows it to become developed. The same may be said of the alleged flatness of foot and increased length of heel of the negro races. The last, though constantly insisted on, is not borne out by anatomical examination, and the idea has probably originated in the altered contour of the back of the leg, dependent on a defective development of the muscles and tendons of the calf.

The modifications of the colour of the skin in different races are well known. We speak of white or black people, but in reality they are all shades of brown, darker or lighter,–a true black skin, according to Professor Huxley's observations, scarcely exists. In the character, as well as the colour, of the hair mankind vary much. The transverse section of the hairs of certain races is flattened, in others it is oval, and, again, in others nearly circular. It is asserted that the first form is characteristic of the Negro, the second of the Aryan, and third of the Mongolian races. In some hair of the first form, the long axis of the diameter gradually changes its position in the length of the hair, causing a crisp curl or spiral twist; this and other peculiarities of the hair are found in widely-separated groups. In connection with the cutaneous system may be mentioned the great accumulations of fat in particular parts of some races, as on the buttocks of the Bosjesmen, more especially the females; and also the great development of the nymphæ in some negro tribes.

The number of the cervical vertebræ in the human skeleton appears to be constant. A variation in the number of the dorsal vertebræ is not unfrequent, but it is usually more apparent than real, being caused by the development of a moveable rib on the first lumbar, thus increasing the former series at the expense of the latter. A truly additional lumbar vertebræ has occasionally been met with. An increase of the number of the sacral vertebræ from five to six is not very uncommon. This may be occasioned by either one of three ways: the interposition of an additional bone into the series, or the annexation by alteration of its characters, and anchylosis of the last lumbar or first coccygeal vertebra. The modification of the last lumbar vertebra so as to bear more or less resemblance to part of the sacrum appears to be of rather frequent occurrence among the lower races, as it may be observed in the skeleton of the Bosjes woman and female Australian in the College Museum, and in a male Australian in the Middlesex Hospital Museum.

The pelvis undergoes modifications of a very interesting nature in different races of men–modifications, however, which chiefly affect the male sex. It may be stated generally that the pelvis of the negro is in all its dimensions proportionally less than is that of the European, and in the Aus[344]tralian this diminution is carried further. While the form and dimensions of the lower outlet of the pelvis is pretty nearly the same in the females of all races, this outlet is greatly diminished in breadth in the male Australian, so that among these people the pelvis of the two sexes present a most remarkable contrast. In the African negro the difference is not so marked. There appears also in the lower races to be a certain tendency towards the narrowing of the transverse as compared with the antero-posterior diameter of the brim of the pelvis. The female Bosjesman's skeleton in the College Museum presents the great peculiarity of an antero-posterior actually greater than the transverse diameter.

The form of the skull undergoes great modifications in different races. When the cranium is elongated and narrow, so that the transverse diameter is less than seven-tenths of the antero-posterior diameter, it is called "oblong," and the race or individual to which it belonged is "dolicho-cephalic." When the transverse diameter is from seven-tenths to eight-tenths of the length, the cranium is "oval." When the transverse diameter is more than eight-tenths, it is "round," or "brachy-cephalic." As a general rule, though, as is well known, the exceptions are numerous; the oblong skull is met with best developed partly among the Scandinavian races and partly among the West African negroes. The oval skull is characteristic of the so-called Aryan races, including the inhabitants of Central Europe, Persia, and the higher races of Hindoostan. The round skull is found among the typical Mongolians, occupying the central parts of Asia, and the aborigines of America. In the long-headed races the cranium is frequently raised in the middle in a ridge, constituting the so-called boat-shaped, or "scaphoidal" skull. Among the Greenlanders it is pyramidal; and there is yet another form which may be described as the "depressed" skull, characterised by its considerable length and breadth, great vertical depression, and large development of the infra-orbital ridges. Of this form there are some very good examples in the Museum from natives of Port Adelaide, South Australia. The internal capacity of the human skull varies greatly, ranging in normal healthy adults from 50 to 110 cubic inches. The variation between the proportion of the greatest internal cerebral length to the length of the basi-cranial axis (from the hinder part of the basi-occipital bone to the junction of the presphenoid with the ethmoid) is also great, the proportion in the higher races of the former to the latter measurement being as 270 to 100, while among the lower races it is but as 230 to 100, indicating a smaller development of the cerebral chamber as compared to the base of the skull and face.

[369]

In this lecture the account of the variations of human structure was resumed. Daubenton was the first to point out that the position of the occipital foramen, in man situated near the centre of the skull, gradually recedes backwards as we descend through the animal series, and that the plane of the foramen, at first horizontal, gradually becomes more oblique, and at last vertical. The best way to measure this is to bisect the skull in the longitudinal and vertical direction (without which no examination can be made with any approach to completeness or exactitude), and then draw a line from front to back in its greatest length, and let fall another at a right angle with this, through the middle of the occipital condyles. The point at which the line drawn through the condyles meets the longitudinal diameter varies greatly in the human species, both in individuals and races. In a well-formed European skull, the space behind the condyles being represented by 100, that in front will be about 115, but it has been found to reach 140, though this is very uncommon. In the lower races, on the [370] other hand, 100 to 140 represent a very frequent proportion between the parts of the cranium thus divided. M. Gratiolet has pointed out a difference in the order in which the sutures become obliterated, the coronal and sagittal disappearing sooner than the inferior sutures in the lower races, and vice versâ; but this remark requires a larger basis of observation before it can be accepted. The different planes in the interior of the skull, mentioned in the first lecture, vary considerably in different individuals, but their variations have not been shown at present to accompany any marked difference of race; it is important, however, to remember that variations may exist. The plane of the squama occipitis also varies extremely, sloping sometimes backwards and sometimes forwards from the superior curved line on the occiput, corresponding with the development of the posterior lobe of the brain.

The development of the face and jaws, in proportion to that of the cranium, is a very important point of difference in various races of men. The determination of their proportions by the facial angle of Camper is not very successful, as the points chosen for its measurement are not relatively fixed. The best method is to bisect the skull, and find the cranio-facial angle, or the angle formed by the basi-cranial axis (from the posterior end of the basi-occipital to the junction of the presphenoid and ethnoid), with a line drawn from the last-named point to the anterior extremity of the premaxilla. It will be seen, by comparing sections of different skulls, that this angle varies greatly, the face undergoing a kind of rotation on the skull; when the angle is open, the jaw projects, giving rise to what is termed "prognathism;" when it is nearer a right angle, the skull is "orthognathic." But projection of the jaw is not only caused by great angulation of the face; the actual size of this part of the skull ("macrognathism"), as compared with the cranial part, must also be taken into account. The jugal arch differs very greatly in size, strength, and later projection; when a skull is held at arms length, with the vertex towards the observer, in some cases the arches are seen projecting beyond the sides of the cranium; such skulls Mr. Busk proposes to call "phanozygous." In well-informed European skulls the chin is straight, or projects beyond the level of the incisor teeth; in the lower races it retreats somewhat, though the recession appears greater than it really is, in consequence of the prominence of the teeth in these races. The arch formed by the teeth in the European, and especially in the short-headed races, is wide and evenly rounded; in some of the lower forms it becomes prolonged and narrow, the sides being nearly parallel. In the lower races the posterior molars are not so disproportionately smaller than the others, as in the higher groups.

Passing from the skeleton, it will be necessary to point out a few of the variations which have been observed in the arrangement of the muscles of the extremities,–a subject which has not been sufficiently attended to, considering the vast opportunities afforded by the dissecting-rooms of our numerous Medical schools. If teachers or students would take the trouble to note all such deviations from the normal structure as may come under their observation, they would render great service to the science of anatomy. In the hand, the flexor pollicis proprius sometimes divides into two tendons, one of which goes to the index finger; sometimes the extensor minimi digiti gives a second tendon to the fourth digit. The extensor indicis is occasionally absent, and sometimes the extensor minimi digiti gives a second tendon to the fourth digit. The extensor indicis is occasionally absent, and sometimes sends a tendon to the third digit; in some rare cases, short extensors have been seen in the hand, and the interossei of the second space have been observed to assume the same arrangement, as to their origins, as those of the foot. In the foot the tibialis anticus is not uncommonly divided into two muscles at its lower end, one inserted into the entocuneiform bone, and one into the first metatarsal; there are sometimes one or two additional peronei passing behind the malleolus; the flexor brevis not unfrequently arises only partly from the calcaneum, the slip for the fifth toe coming from the deep flexor tendon. It appears from these instances that the hand may occasionally assume some of the characters of the foot, but there is no evidence yet to show that the foot ever does the same to the hand.

The brain of man varies greatly in size, weight, and form; perhaps no part of it so much as the posterior lobe, as may be seen in the collection of casts of the interior of crania lately added to the College Museum. There seems no relation between the projection of this lobe and the position of the individual in the scale of human beings; on the whole, it seems as great or greater among the lower than in the higher races. The posterior cornu and hippocampus minor among the internal structures are the most variable, the former being merely a relic of the great original cavity, its greater magnitude would indicate a low, rather than a high condition. The hippocampus minor is constant; but its appearance in the ventricle, being entirely dependent upon the form and size of the cavity, varies greatly. A great range may be observed in the complexity of the convolutions in different brains. On the whole, they are simpler in women than in men, and in the lower races the convolutions have a greater simplicity and symmetry than in the higher. Gratiolet called attention to this in his description and figures of the brain of the Bosjes woman who died at Paris, called the "Hottentot Venus," and though it has lately been asserted that this person was an idiot, there is the best possible evidence to show that such was not the case. Recently Mr. Marshall has obtained from the Cape the preserved brain of another female of the same race, and his description it, communicated to the Royal Society, fully bears out Gratiolet's conclusion.

The important question now remains, what is the value of the differences which have been shown to exist in the structure of human beings? This resolves itself into two other questions,–1. Are they sufficient to justify us in supposing them to indicate different species of men? 2. Can any of the deviations be considered as transitional towards the lower forms of animals? In respect to the first, it is certain that well-defined types occur in different geographical localities; those whose characters are most distinct are,–European or Caucasian; 2. Mongolian; 3. Negro or Ethiopian; and 4. Australian. That these types are observable and distinct there can be no doubt, and any zoologist taking a well-marked example of each, without any other evidence, would pronounce them distinct species; but extended knowledge shows that every intermediate form can be found between the most typical, and there is no proof that they are not all fertile, not only inter se , but the resulting race is also fertile. These two considerations conclusively show that there is no foundation whatever for the doctrine of the diversity of mankind; the well-marked varieties may be called races , but not species . As to the second question, it may be answered equally conclusively. Although, here and there, as in the lower races of men now upon the earth, and in the skeleton found in the cavern in the Neanderthal, the human type varies a little in some particulars in the direction of the Ape, the extent of this variation is very slight indeed, when compared with the whole difference which separates them, and it may be safely affirmed that there is at present no evidence of any transitional form or intermediate link between Man and the next succeeding forms in the vertebrate scale.

[398]

Having concluded the sketch of the anatomy of man, Professor Huxley passed in this lecture to a description of the structure of those animals which approach most nearly to him. These are by universal consent admitted to be the gorilla, the chimpanzee, the orang, and the gibbon. How far they resemble, and in what respects they differ from man, and which approaches nearest to him, will now be considered, the chimpanzee being taken first, because of its anatomy we have the fullest illustrations in the College Museum.

This animal, Troglodites niger of the zoologist, is an inhabitant of the West Coast of Africa, ranging from Sierra Leone to Congo. Trustworthy information as to its habits in its native state is scanty, but it appears to live in small families or troops, and to be essentially arboreal in its nature, only occasionally descending to the ground. When it does so, it sometimes for a short time assumes the erect posture, but its usual position in walking is semi-erect, the body inclined, the soles of the feet flat on the ground (the outer edge brought down first), and the hands bent, so that the knuckles form the point of support for the fore-limbs. It builds a kind of nest of branches and leaves, lives entirely on vegetable food, and is, on the whole, of a timid and gentle disposition, especially when young, though the adult males can use their powerful canine teeth as weapons of offence and defence. The intelligence of the young specimens which have lived in confinement in this country has often been remarked upon.

When full-grown, the chimpanzee probably never exceeds four feet four inches in height. The proportions of its body differ widely from those of man. When erect, the middle point of the vertical height is three or four inches above the symphysis pubis, indicating the relative shortness of the lower limbs. The upper limbs, on the other hand, are so much longer than those of man that the extremities of the fingers reach below the knees, and the extreme span measures about seventy inches, the height being only fifty. The forearm is nearly equal in length to the humerus; the tibia is longer in proportion to the thigh than in man; the thigh bone and humerus are of nearly the same length. In all these proportions it will be remembered that there was a slight variation between the higher and lower races of man, and that in the latter they deviated from the normal standard in the same direction, though in an infinitely smaller degree, as now shown to be characteristic of the chimpanzee. The hand and foot are nearly of the same length, the former being, if anything, somewhat longer. The palm and the sole are remarkably narrow. The tarsus, metatarsus, and digits are of nearly equal length, the middle segment being rather the shortest. The heel is much shorter than in man. The distal segment of the tarsus rotates freely on the proximal part, being much less solidly united than in man.

Among the external features may be noted the ears, very large, but preserving all the essential parts of the human ear, except that the antihelix is rather less marked. The nose is flat, the nostrils look downwards, and the septum between them is narrow. The thumb is very short, reaching only to the base of the first phalanx of the index finger. Perhaps the most striking character is that the great toe is greatly devaricated from the others, and partakes of that thumb-like appearance which gave rise to the name of Quadrumana applied to the whole group of monkeys. The colour of the integument is a pale brown. The hair is black, abundant in the scalp, and, contrary to what obtains in man, more developed on the dorsal than the ventral surface of the body; on the arms and legs its disposition is similar to that of man, converging towards the elbow, and sweeping away from the knee-joint. There are distinct eyebrows, eyelashes, and whiskers; the beard and moustache are exceedingly scanty and of a pale colour. The penis is altogether external and pendulous, the scrotum placed behind its root, and the mammæ are pectoral.

The skeleton presents the following important characters:–The vertebral column is comparatively straight, for though it possesses all the curves observed in the human body, they are far less marked. The same holds good with the vertebro-sacral angle. The cervical vertebræ are seven in number. The dorsal and lumbar taken together are seventeen, as in man; but there is a thirteenth rib, so that they are reckoned as thirteen dorsal and four lumbar, instead of twelve dorsal and five lumbar. The spines of the cervical vertebræ, instead of diminishing in length in the middle of the series, are nearly equal, and except in the dentata are but slightly, or not at all, bifid. The last lumbar vertebra, as a general rule, unites with the sacrum and iliac bones in the adult animal; this character was met with as an anomaly in the human subject, more frequent in the Australian and African races than in Europeans. The sacrum differs greatly from that of man, in being narrower and more elongated from above downwards. The sacral and coccygeal vertebræ, together are from ten to twelve in number, the upper five generally coalescing to form the sacrum. The coccygeal vertebræ continue the line of the curve of the sacrum as in man. Of the ribs seven are true, or articulate directly with the sternum, and six are false. The sternum much resembles that of man, being flat and broad. The thorax generally is longer from above downwards, and deeper from before backwards, than in man.

The skull presents in its external form some obvious and striking differences from the human skull, especially the small mass of the cranium compared with that of the face, the prominence of the supra-orbital ridges, and the great projection of the jaws. A longitudinal section shows, however, that these differences appear greater externally than within; and as previously shown, there is among the lower races of men a tendency to approach them. The cranial capacity of the largest chimpanzee measured is 27-1/2 cubic inches, that of the smallest normal adult man being 55. The cerebral length to the floor of the skull (basi-cranial axis) is as 180 to 100. The occipital foramen is situated further back than in any human skull, the length in front to that behind the condyles being as 258 to 100. The plane of the occipital foramen has an upward inclination. The olfactory and the tentorial planes are still nearly horizontal. The squama occipitis is inclined upwards and backwards from the superior curved line, but this is placed higher on the occipital bone than in man. The great projection of the supra-ciliary ridge is connected with the large development of the frontal sinuses. The crista galli is small or absent. The ethmoid fossæ are not deeply sunk. The orbits are very large, their roofs pushed up into the skull considerably diminish the size of the cranial cavity in this region. The ethmoid and presphenoid unite together without being covered over by the frontal; in this character man and the chimpanzee agree, and differ from others of the anthropoid apes. The upper edge of the squamosal is straight, and unites with the frontal, so that the alisphenoid does not join the parietal; this is sometimes the case also in the human subject. There is no deep fossa on the inner surface of the petrosal for the lodgment of a portion of the cerebellum. The mastoid prominence is of very different form from that of man, and there is no trace of an ossified styloid process. The middle root of the zygoma is greatly developed. The jugal arch is so much developed in proportion to the cranium that the skull is much more phænozygous than any human skull. The sutures of the cranium disappear at a comparatively early period. The jaws are larger in proportion to the cranial cavity, and project more forward than in man, so that the chimpanzee is both macrognathous and prognathous. The cranio-facial angle is about 120°. The chin is entirely wanting in the lower jaw. The anterior nasal spine, which rises up from the pre-maxillary in man, is entirely absent. The shape of the palate differs from that of man; its sides are [399] straight, being, if anything, wider behind. On the middle of its posterior border there is a spine projecting backwards. The sutures between the pre-maxillary and the maxillary bone does not become obliterated till the commencement of the second dentition. The nasal bones lose their distinctness very early; but as long as they remain separate are seen to be flat and broad, and rather contracted in the middle.

[428]

Anatomy of the Chimpanzee Continued.–The scapula is of an elongated and narrow form, compared to that of man, and has a very clearly defined articular surface on the acromion for the clavicle. The last-named bone much resembles in its curves and general form the human clavicle. It articulates very obliquely to the manubriam sterni, so that the outer rises greatly above the level of the inner extremity, causing the characteristic high shoulders and apparent shortness of the neck, for, contrary to what is generally supposed, the cervical region is not really shorter proportionately to the trunk than in man. The humerus, radius, and ulna closely resemble the same bones in the human subject, with the alterations of proportion already noticed. The radius is rather more curved, giving a wider interosseous space. There is no essential difference in the structure of the carpus from that of man, the bones have the same number and relations to each other, but they present slight differences of form and proportion. The trapezium is a smaller bone, and its articular surface no longer presents the characteristic saddle-shape found in man, but is a simple, oval, convex facet, in relation to the comparative small size and less important function of the thumb itself. The fingers are of much greater length, compared with the breadth of the hand, than in man, and the phalangeal bones are more curved. These modifications of the hand of the chimpanzee show that it is an organ less adapted for administering to the will, exercising the sense of touch, and the multitudinous purposes to which it is put in man, but have clear reference to its principal purpose as a scansorial organ.

The pelvis differs greatly from that of man. Though the whole animal is smaller, the pelvis is absolutely of greater length. The iliac bones are much narrower in proportion, and the whole has little of the basin-shape characteristic of the human pelvis. The front surfaces of the ilia are certainly somewhat concave, and traces of the sigmoid curvature of the upper margin are visible. The sacro-iliac angle is more acute than in man, not exceeding 70°. The pubic symphysis is singularly long, and the union of the bones very complete.

The antero-posterior diameter of the pelvis greatly exceeds the transverse diameter, contrary to what generally obtains in man, and another important point of difference, and approximation to the lower monkeys, is the eversion of the tuberosities of the ischia. The femur is of small size, but not otherwise unlike that of man; the internal condyle, however, scarcely projects further than the external. In the ankle-joint, the astragalus is embraced firmly by the projecting malleoli; but the lower articular surface of the tibia, instead of being horizontal, slopes obliquely upwards to the outer side. In the foot, the extremely different proportions of the tarsus, metatarsus, and digits from those of man have already been alluded to; the metatarsal segment being rather the shortest of the three. The various bones of the tarsus have fundamentally precisely the same number, form, and relations, but the differences in detail are numerous. The hinder process of the calcaneum is much less developed than in man, and its tuberosity is single and narrow at its inferior extremity–circumstances which greatly impair the efficiency of the foot as an organ of support. The scaphoid and cuboid bones rotate freely on the astragalus and calcaneum, and it is on account of this mobility, and not from any peculiarity of the ankle joint, that the outer side of the foot comes to the ground first when walking, and that the soles naturally turn inwards when the foot is at rest, or in climbing. The phalanges of the toes exhibit a certain concavity of the under surface, but not so marked as in the fingers. But the greatest peculiarity of the foot, and one which makes it pre-eminently adapted for grasping boughs in climbing, is the position and mode of articulation of the great toe. This is one of the most interesting examples in nature of a very slight modification of the structure of parts essentially the same producing a vast change in their function. The change is in the articular surface of the entocuneiform bone–a change the converse to that which takes place in the trapezium. The result is that the toe is freely moveable, though not in the same direction as the others, being opposable to them, and the peroneus longus muscle, having precisely the same origin and insertion as in man, has its function reversed, and instead of steadying the leg from a fixed point below, becomes a powerful adductor of the great toe, affording prodigious grasping power to the foot.

Leaving the skeleton, Professor Huxley passed to the consideration of the muscular system, confining his observations to the upper and lower limbs, of the muscles of which he had lately, in conjunction with Mr. Flower, made a new and careful dissection. There are certain muscles which the chimpanzee possesses, which are not found in man. These are:–1. A muscle passing from the transverse processes of the upper cervical vertebræ to the outer end of the clavicle, called "levator claviculæ" by Tyson, and "trachelo-acromial" [429] by Duvernoy. This muscle, however, does not seem to be always present even in the Chimpanzee. 2. The "dorsoepitrochlear" of Duvernoy, a muscular slip passing from the tendon of insertion of the latissimus dorsi to the elbow. 3. The "scansorius" of Trail, arising from the edge of the ilium, and inserted into the great trochanter, a powerful internal rotator of the leg. 4. A very small muscular slip, arising from the calcaneum, apparently detached from the abductor minimi digiti, and ending in a tendon inserted into the base of the fifth metatarsal bone, which might be called "abductor ossis metacarpi quinti." Now, these muscles, though stated to be absent in man, are not wholly unrepresented, either normally or exceptionally. 1. A separate bundle has been seen to pass from the mastoid process to the extremity of the acromium, detached from the trapezium, and representing to a certain extent the trachelo-acromial of the inferior mammals. 2. According to Henle, the triceps extensor of the arm has constantly a tendinous slip from the latissimus dorsi, constituting an interesting approximation to the dorso-epitrochlear. 3. A distinct muscle arising in front of the gluteus minimus near to the sartorius, and either joining the tendon of the gluteus or inserted separately into the femur, and so resembling the scansorius of the apes, has been observed in man. 4. Although not hitherto noticed in anatomical works, Mr. Wood has frequently seen in the human foot a muscle precisely corresponding to that above described under this head.

There are certain muscles which are developed in man, and which either are, or are commonly said to be wanting, in the chimpanzee. These are–1. The extensor primi internodii pollicis; 2. The peroneus tertius. Instances of the absence of both these muscles in man have been met with–the latter, especially, is very variable. The transversus pedis and the extensor indicis have both been said to be absent in all apes; but, on the contrary, they are really well developed in the chimpanzee, and as we shall afterwards see, in other members of the group. The flexor accessorius was absent in the specimen recently dissected, but it has been found by other observers.

Certain muscles differ from the same muscles of man in their origin. The soleus rises only from the fibula by a tendinous head. The flexor brevis of the toes arises partly from the calcaneum, and partly from the under surface of the tendon of the long flexor, the division for the fourth and fifth digits having the latter origin. This remarkable simian modification is, however, met with occasionally, and in a limited manner, in the human foot, the muscles furnishing the perforated tendon for the fifth toe having been seen to arise from the tendon of the long flexor, apart from the remainder of the short flexor.

[456]

Anatomy of the Chimpanzee Continued.–Professor Huxley commenced by stating that since his last lecture Mr. John Wood had shown him drawings which he had made of a true "levator claviculæ," and also of an "abductor ossis metacarpi quinti" occurring in the human subject. He then proceeded to the consideration of certain muscles of the chimpanzee, which differ essentially in their insertion from the corresponding muscles in man. These are,–1. The pectoralis minor, which varies much in insertion in different chimpanzees which have been dissected; in Duvernoy's specimen it was attached to the coraco-clavicular ligament; in Wilder's, to the coracoid process on the right side, and the great tuberosity of the humerus on the left; in the one lately dissected by Professor Huxley and Mr. Flower it joined the tendon of the supraspinatus muscle. In man its insertion is not constantly into the coracoid process. 2. The flexor longus pollicis of the chimpanzee presents a remarkable deviation from that of man. Arising in the usual manner, it gives a very slender tendon to the thumb, and a much larger, stronger tendon, which is the perforating flexor tendon of the index finger. The flexor profundus digitorum supplies only the third, fourth, and fifth fingers; in the palm of the hand the two tendons are closely united. The nearest approach to this arrangement which has been observed in the human subject is seen in those cases in which the flexor pollicis longus has given a slip to the tendon of the flexor profundus which goes to the index finger. 3. The gluteus maximus departs considerably from that of man, the nature of the departure chiefly having relation to the different attitude assumed by the chimpanzee. It is small and flat, causing little prominence of the buttock, and from its lower edge the muscular fibres are continued down on the outside of the thigh as far as the external condyle of the femur. This part was described by Duvernoy as a separate muscle, under the name of "ischio-femoral." 4. The two long flexors of the toes, the flexor hallucis and the flexor digitorum, cross each other as usual, and then divide into several tendons, the former supplying the hallux and the third and fourth digits, the latter the third and fifth digits; at their point of division they are partially blended together. It will be recollected that when describing these tendons in the human foot, it was demonstrated that the flexor hallucis joined in the supply, to a variable extent, of the second, third, and fourth toes, so that difference in the arrangement of these tendons in man and the chimpanzee is only a difference of detail.

There are certain muscles which are single, or nearly so, in man, but which are more or less divided into two in the chimpanzee. 1. The extensor minimi digiti appears to be constantly divided in the chimpanzee, one tendon going to the fourth, and the other to the fifth digits. This is, however, a not uncommon exceptional condition in man. 2. The extensor ossis metacarpi pollicis is a more or less completely double muscle in the chimpanzee, one tendon being inserted into the trapezium, and the other into the bases of the metacarpal bone of the thumb. In man, as we have seen, the tendon is commonly divided for some distance from its insertion. 3. The tibialis anticus undergoes the same change in the chimpanzee–the division of the tendon observed commonly in the human foot being carried up into the muscular fibres, sometimes quite to their origin, so that the anterior portion has been described by Cuvier and other anatomists as a distinct muscle under the name of abductor hallucis longus. 4. In the interossei of the hand, the division which was noticed in man at their anterior extremity, one tendon being inserted into the base of the first phalanx, the other into the extensor tendon, is carried to a greater extent, each interosseous muscle of the human hand being represented by two distinct muscles in the chimpanzee, having in both cases precisely the same insertions.

The general result of this sketch of the myology of the limbs of the chimpanzee as compared with those of man, is to show a certain difference between the two, but in almost every case the differences found in the chimpanzee, are either exaggerations of arrangements existing normally in man, or they are arrangements which are met with in him occasionally as varieties.

Some questions now remain of much interest, and about which much discussion has taken place of late. Is the terminal division of the fore-limb of the chimpanzee properly to be called a hand? and secondly, is the terminal division of the hind-limb to be called a foot or not? These questions have acquired their interest thus:–Tyson, a hundred and fifty years ago, struck by the great external resemblance of the hinder limb with its opposable thumb to a hand, remarked that these animals might be called "quadrumanous." The term was afterwards made use of in a technical sense by Blumenbach, Cuvier, and others, and it has frequently been said that the great distinction between man and apes was, that the former possess two hands and two feet, and the latter four hands. In the consideration of this question, it will be necessary first to settle the basis of the argument. If the grasping power conferred by an opposable digit be taken into consideration, we must call the terminal division of the hind limb of a bird or an opossum a hand equally with that of a monkey; but morphological analogies cannot be decided by physiological function, only by an exact comparison of the [457] essential anatomical characters. We have seen that the terminal division of the fore-limb of the chimpanzee resembles the hand of man in all its essential muscular arrangements: it has, 1, long flexors and extensors; 2, a distinct extensor indicis; 3, an opponens pollicis; 4, the divaricators fundamentally disposed as in man. It differs from the hand of man in, 1, the union of the flexor pollicis and indicis; 2, the absence of an extensor primi internodii pollicis; 3, the division of the extensor ossis metacarpi; 4, the division of the interossei. The first and third are in some sense an approximation to foot arrangements; the second and fourth are special aberrations; but on the whole the differences are very unimportant, as compared with the great resemblances admitted on all sides; and, therefore, the term "hand" may properly be applied to this part in the chimpanzee.

If we examine in the same way the myology of the terminal division of the hind limb, we find it agreeing with the foot of man in the following characters:–1, the presence of a short flexor and extensor; 2, the intermingling of the long flexor tendons; 3, the presence of a peroneus longus; 4, the absence of a special extensor of the fifth digit; 5, the absence of an opponens hallucis, and presence of an opponens minimi digiti; 6, the single tendon of the interossei inserted into the first phalanx; 7, the presence of a transversus pedis; 8, the occasional presence of a flexor accessorius. On the other hand, there are the following deviations from the arrangement of the foot in man:–1, the more extensive division of the tibialis anticus; 2, the absence of the peroneus tertius; 3, the presence of a special abductor ossis metacarpi quinti; 4, the frequent absence of the flexor accessorius; 5, the origin of part of the short flexor from the deep flexor tendons; 6, the looseness of union of the flexor hallucis and flexor longus digitorum tendons, and the slight difference of their distribution; 7, the different distribution of one of the dorsal interossei. The greater part of these differences are, as we have seen, either differences of degree or occur as occasional varieties in the human foot, and they have no manner of weight when compared with the great resemblances; they are certainly not relatively greater than those found between the hand of man and the hand of the chimpanzee. Therefore, the same process of reasoning which induces us to call the terminal division of the fore-limb of the chimpanzee a "hand," must also compel us to call the corresponding part of the hind-limb a "foot." If we revert to the osteological structure we shall find that the argument acquires even greater weight, and we must conclude that there is not the smallest ground for applying the term "four-handed" to the apes, if it is meant to imply by that term that there is any structural difference between their foot and that of man.

[486]

The Anatomy of the Chimpanzee continued.–The larynx of the chimpanzee has all the essential parts of the same organ in man, every cartilage, ligament, and muscle being represented, with only differences of detail in form and proportion. There is, however, connected with it a very singular exaggeration of a structure existing in man, the so-called sacculus of the larynx. This undergoes on the left side a most remarkable enlargement in the adult chimpanzee, forming a pouch which extends beneath the sterno-thyroid and sterno-hyoid muscles, into the anterior triangle of the neck, and even projecting into the axilla. The function of this great air-sac is entirely a matter of speculation at present.

The chimpanzee has the same dental formula as man –viz.,

The teeth agree with those of man in some of their most characteristic features. Of the incisors, the median pair in the upper jaw, and the outer pair in the lower jaw are the largest; the upper premolars have two cusps, or which the external is the most developed; the lower premolars have two cusps united by a transverse ridge; both the upper and lower molars have the same pattern as those of man, but in a marked and exaggerated form. The teeth also present the following differences from those of the human subject:–The arrangement of the alveolar arch in both jaws vastly exaggerates the peculiarity found in the lower races of man, the sides being quite parallel, or even slightly concave externally; the absolute size of the teeth is greater in the chimpanzee than in man; the upper where it is prominent and pointed as in the carnivora, though only used as a weapon of offence and defence, not in securing prey. The lower canine, though smaller, projects above the others of the series, and its axis is obviously anterior to the upper one, and there is an interspace to receive it between the latter and the contiguous incisor. The anterior premolars or the lower jaw present a certain declivity of the front edge, which is an approach to the very peculiar form of this tooth in the lower apes. The premolars of the upper jaw are implanted by three, those of the lower jaw by two fangs, thus presenting a considerable difference in this respect from the [487] human subject. In their mode of wear the teeth present peculiarities observed in the lower races of men, the incisors bite directly one against the other, and become ground to a flat surface, and the outer edge of the lower, and the inner edge of the upper molars first show signs of attrition.

In the deciduous dentition we have the essential human characters repeated, with remarkable differences of detail. The first canines are proportionally small, projecting but slightly above the remainder of the series. The pattern of the milk molars of the upper jaw is as in man; in the lower jaw, however, it differs considerably, the posterior tooth especially having only four cusps instead of five. In the order of succession there is a difference from that observed in man. The great canine, appearing to require longer elaboration, does not come into place until after the molar series is complete.

The soft palate has a well-developed uvula. The tongue is very like that of man, except that the circumvallate papillæ, instead of being arranged like a V, are like a T, with the top turned forwards. The salivary caruncle beneath the tongue in the middle line is lengthened out to a point, presenting an indication of the greatly-developed "sublingua" of the lower apes and lemurs. The stomach and cæcum closely resemble those of man in form, and there is a long vermiform appendage. The great vessels arise from the aorta in precisely the same manner as in man.

Of the brain a remarkably excellent account has lately been published by Mr. Marshall, the statements in which Professor Huxley had himself been able to verify in a recent specimen. The largest brain of an adult chimpanzee, judging from the size of the interior of the cranium, is less than half that of the smallest normal human subject, and as shown by casts that were exhibited, very much less than half that of the average Australian or African brain. In Mr. Marshall's young chimpanzee the brain weighed 14 oz.; that of a European child at a corresponding period of dentition being 38 oz. The form of the brain differs from that of man, in being less convex in the parietal region, but more particularly in the great diminution of the anterior portion, which is cut away laterally so as to bring it to a point in front, and greatly excavated beneath in the supra-orbital region. The general divisions of the brain into segments are the same as those before given in the lecture on human anatomy. The olfactory segment bears a striking resemblance to that of man, being thin and flat, and received into a groove on the under surface of the frontal lobe. The cerebral hemispheres agree with those of man in the manner in which they cover all the other parts, so that on looking at their upper surface no portion of the olfactory lobes or cerebellum are to be seen. According to Mr. Marshall, the amount of overlap of the cerebrum behind the cerebellum is greater proportionately to its length than in the average human brain. If we adopt the old division of the hemisphere into three lobes, anterior, middle, and posterior, we find them all represented in the chimpanzee's brain, and agreeing with the definitions given of them in human anatomy. The five lobes of the outer surface, as defined by Gratiolet, can also be distinctly traced. The central lobe, or island of Reil, though more simple, has the same form and is sulcated on the same fundamental pattern as in man. The other lobes present all the sulci and gyri previously described in man, with the following differences of detail:–The principal character by which the Bosjes woman's brain was seen to differ from the European's is here greatly exaggerated; the gyri are much larger in proportion to the brain, are less complex or subdivided, and present more bilateral symmetry. The fissure of Sylvius is less inclined; the fissure of Rolando is placed further forward than in man; the insula is no longer completely covered by the temporal lobe in front; of the annectent gyri only the second, third, and fourth appear on the surface; the first is folded upon itself, giving rise to the external perpendicular fissure, a peculiarly simian character. On the inner face of the hemisphere every gyrus and sulcus seen on the human brain can be traced, the principal differences being the small mass of brain lying above the corpus callosum and the forward inclination of the internal perpendicular fissure.

In the interior anatomy of the brain may first be noticed the smaller proportionate volume of the corpus callosum, although it has all the same parts and general form as in man. The septum lucidum is exceedingly thick, and the precommisural fibres well developed. The lateral ventricles are, in proportion to the size of the brain, as large or larger than in man, and have the same general form. The anterior cornu sends no prolongation into the olfactory lobe. The descending cornu contains the hippocampus major, which frequently shows digitations upon its terminal part; the posterior cornu has the same form and extends as far back as in man and contains within it a well-developed hippocampus minor and collateral eminence, having the same relation to fissures on the surface as in man, as can be most readily demonstrated by transverse sections. No hard bodies have as yet been found in the Pineal gland. There are two distinct corpora albicantia. The cerebellum is singularly like that of man, but is larger in proportion to the cerebral hemispheres; in Mr. Marshall's chimpanzee it was as 1 to 5-3/4, in man as 1 to 8-1/2. Both the width of the cerebellum, and of the nerves coming off from the base of the brain are proportionately greater than in man. Finally, the entire absence of these intervals between the pons and the anterior pyramids called "corpora trapezoidea," found in the lower mammals, may be noted.

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The Anatomy of the Chimpanzee continued.–In the adult male the penis is very small, of a long and slender form, and terminating in a small, narrow glans, of very different form from that of man. On the other hand, the testes are extremely large. The communication between the tunica vaginalis and the abdominal cavity is shut off as in man. The reproductive organs of the adult female have not been described, but in a young example of that sex, the clitoris was very large, the vagina proper narrow, but dilated at the posterior part, the uterus simple having the same general form as that of a child of corresponding age, but differing in being more flattened from before backwards and quite straight.

We have at present no definite knowledge of the changes which take place in the embryo before birth, but the subsequent laws of growth can be readily studied on the collection of skeletons in the College Museum, and give results in some respects very different from those observed in the human subject. The total height of the whole body when full grown is about three times its height at birth. There is the same comparatively small increase in the head as in man, the vertical height of the adult skull not exceeding twice that of the new-born animal. In man we saw a great difference in the relative growth of the legs and arms as compared with each other, and with the trunk, but in the chimpanzee the same proportion is approximately preserved throughout; hence the young chimpanzee and the human child are more alike in form and proportions than are the adults of both species. As regards special segments of the limbs, a different law of growth prevails from that observed in man; the hand and foot are proportionately longer in the young, and as growth advances the other segments increase at their expense. Among other changes which take place in the process of development may be noticed the obliteration of the suture between the maxilla and the premaxilla before the milk teeth are all in place; in this respect the chimpanzee approaches man and differs from all other apes. With growth also comes an immense increase of macrognathism and prognathism, and a great development of the frontal sinus and supra-orbital ridges, which greatly alter the external appearance of the skull.

In the adult state, certain differences are observed between the sexes, independently of those directly connected with the generative function. In the first place, it is to be noted that there is no very marked difference of size between the male and female. In the dentition a striking sexual character is seen in the greater size of the canine teeth in the male. The pelvis presents characters in the two sexes quite parallel to those observed in the human subject. Although of precisely the same vertical height, every other dimension of the female chimpanzee's pelvis is strikingly greater than that of the male, particularly the breadth of the inferior outlet.

Although the number of chimpanzee's skeletons and skulls in our collection is not yet very numerous, it is sufficient to show that there is a considerable range of variation between different individuals. A cast of a skull of a variety called by M. Du Chaillu "Kooloo-Kamba" was exhibited, differing from the ordinary form in the comparatively small size and excavation of contour of the face, great size of cranial cavity, and depth of ramus of lower jaw. It might have been thought to belong to a distinct species from another skull exhibited, if the collection did not furnish several examples directly intermediate in all their characters. Professor Huxley remarked that if the tendency to vary was so strong in this anthropoid ape, that amongst individuals having a very limited geographical area, and subject to the same climatic and other external conditions, we could find skulls differing from each other as widely as those of the European and Australian among men, we should not be surprised to find that man, spread over every part of the globe, should present the range of variation we have seen in his physical characters; nor should we find it necessary, in accounting for such variation, to go back to diversity of origin or difference of species.

The Gorilla (Troglodytes gorilla ) inhabits the same tract of country as the chimpanzee, but is perhaps not so widely spread. It lives more in the hilly inland parts than the chimpanzee; when on the ground it readily assumes the erect posture; its stentorian howl can be heard at a great distance, and the old males are very ferocious. Little more than this is known of its habits. The stature of an adult male, when placed upright, is about five feet, perhaps never exceeding five feet six inches. The colour of its hair is blackish-dun; in old specimens grey. The integument of the exposed parts of the face, etc., is not pale, as in the chimpanzee, but black. The manner in which the hair is distributed is much as in the chimpanzee. The general proportions of the body are also very like those of that animal, the length of the arms being about two-thirds of the height, the legs two-thirds of the [510] arms, and the height two-thirds of the span from tip to tip of the extended fingers. In minor respects there are differences of proportion from those of the chimpanzee. Thus, the humerus is longer than the radius, instead of being nearly equal, and the hand is much shorter in proportion to the forearm and humerus. The dimensions in the male gorilla's skeleton in the College museum are–Humerus, 17 inches; radius, 13; hand, 9-1/2. The foot is very distinctly longer than the hand; the great toe is proportionally stouter than in the chimpanzee: the sole of the foot and palm of the hand are extremely broad, and there is a very marked syndactyly of the toes and fingers, extending as far as the end of the first phalanx. The nose is somewhat more projecting than in the chimpanzee, the external ear differs in being very much smaller.

The number of the vertebræ of the different regions of the spine are the same as in the chimpanzee, viz., cervical 7, dorsal 13, lumbar 4, sacral 5, coccygeal not satisfactorily determined. The cervical vertebræ are remarkable for the great elongation of their spinous processes, for the attachment of muscles to support the great weight of the head and jaws. The last lumbar vertebra has its lateral processes expanded and united with the sacrum. The thorax is of great size, the sternum broad and flat; the space between the last rib and the crest of the ilium is very small.

In no part of the organisation of the gorilla is its difference from man so apparent as in the skull. This, however, is more apparent than real, as the true characters of the brain case are completely hidden by the prodigious development of the lambdoidal and sagittal crests and the supra-orbital ridges. The capacity of the largest cranium of a gorilla yet measured is nearly thirty-five cubic inches. In this respect, and the greater development of the mastoid process, the gorilla's skull approximates more than the chimpanzee to the human subject. In all other characters it approaches more to the lower apes, especially the baboons. One of the peculiarities belonging to the latter division is the union of the frontal bone across the base of the skull, covering the junction of the presphenoid and ethmoid, and causing the olfactory fossa to become narrower and more funnel-shaped.

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Anatomy of the Gorilla continued.–The facial portion of the skull is slightly more prognathous and macrognathous than that of the chimpanzee. The jugal arch is considerably stronger and more curved. The palate is longer and narrower. An interesting character (not being an adaptive modification, but a mark of serial degradation) is the late disappearance of the suture between the premaxilla and the maxilla, which remains open up to adult age. In the lower jaw the great depth and massiveness of the rami and the entire absence of any mental prominence may be noted. The body of the hyoid bone forms a more considerable cup-shaped cavity than in the chimpanzee; its greater cornua are well developed, the lesser cornua rudimentary.

The scapula of the gorilla is markedly more like that of the human subject than is the chimpanzee's. The coracoid process is strong and curved. The humerus is longer than the radius; the radius itself has a strong curve. The hand in its fundamental construction resembles that of man and the chimpanzee; where it differs from the latter it is generally in the direction of the human type. The thumb is longer and stronger in proportion to the hand than in the chimpanzee, and the form of the trapezium is more like that of man. The pelvis has the great depth, the obliquity of the upper aperture, the great length of the antero-posterior, as compared with the transverse diameter, the long symphysis pubis, and the eversion of the ischia characteristic of the ape. It approaches the human type somewhat, however, in the great width of the ilia. The femur is somewhat more like that of man than the chimpanzee's. The articulation of the astragalus with the tibia has the same obliquity as in the chimpanzee, but the bone itself is stronger and broader. The calcaneum projects rather further backwards, but retains its narrowness and the single tubercle. The entocuneiform bone has the characteristic ape form. In the proportion of the different regions of the foot there is a slight approximation to man, which is lost, however, in the proportionately shorter hallux. On the whole, though with certain exceptions here and there, where the gorilla departs from the chimpanzee in the character of its limbs it approaches man, while in the skull it comes nearer to the lower apes, so that it is by no means an easy question to decide which of the two animal forms the nearest approximation to man in its osteology. Perhaps the greater relative size of the cranial cavity inclines the balance in favour of the gorilla.

The dentition is essentially the same as in man and the chimpanzee, but deviating further from the former in the immense development of the upper canines, and in the greater relative size of the posterior inferior molars. The milk teeth closely correspond with those of the chimpanzee, as does the order in which the teeth succeed each other, the permanent canine being the last in place.

Our knowledge of the myology of the gorilla is at present very defective, being derived chiefly from Duvernoy's dissection of one individual, supplemented by some original observations of Professor Huxley on the muscles of the hand and foot. Taking them in the same order as was done in the case of the chimpanzee, first, may be considered those muscles of the limbs not commonly found in man and stated to be present in the gorilla. These are the dorso-epitrochlear and the levator [538] claviculæ; the scansorius is not mentioned by Duvernoy. 2. Those muscles existing in man, but which have not been hitherto found in the gorilla. The subclavius was only represented by a ligament. The plantaris, extensor primi internodii pollicis, and the peroneus tertius were all absent. The two last appear to be constantly wanting in the apes. 3. Muscles commonly said to be absent in the apes, but which are found in the gorilla. The transversus pedis is powerfully developed, arising by three bundles from the heads of the second, third, and fourth metarsal bones. The extensor indicis is perfectly distinct, giving no division to the other digits. The extensor minimi digiti goes altogether to the little finger. 4. Muscles which differ from those of man in their origin. The most important of these is the flexor brevis digitorum; the portion which arises from the os calcis gives the perforated tendons to the second and third toes; the remainder arises by two fleshy bellies from the surface of the long flexor tendon. The tendon for the fifth toe is not perforated, but runs to the outer side of the deep tendon. The soleus arises by a single head from the fibula. 5. Muscles which differ from those of man in their insertion. Duvernoy found the flexor pollicis longus represented by a small tendon from the flexor profundus digitorum going to the thumb as in the chimpanzee. Prof. Huxley found the tendon on the palmar surface of the thumb, but on tracing it upwards, it did not appear to join the other flexor, but ended by spreading out in the fascia of the palm, and was partly inserted into the trapezium and first metacarpal bone, so that, functionally, the muscle may be said in this instance to have been absent. In the foot the long flexors have essentially the same arrangement as in the chimpanzee, the flexor digitorum goes to the second and fifth digits, and the flexor hallucis to the first, third, and fourth, with only a slight intermingling of their fibres. The flexor accessorius is well developed, with its ordinary connections. 6. Muscles which are single in man, but divided in the apes. The division of the tendons of the tibialis anticus and extensor ossis metacarpi pollicis, so marked in the chimpanzee, was found in the gorilla not to extend higher than in man.

The gorilla's hand and foot afford through their great size very fine illustrations of the arrangement and action of the interossei and lumbricales. The latter are four in number in the hand, and are inserted into the extensor sheaths as usual; in the foot there are but two. The interossei of the hand agree in the main features of their arrangement with those of the human hand, being double on each side of every finger, the more dorsally placed muscles are inserted into the side of the base of the first phalanx, and the others send their tendons into the extensor sheath, and form the chief extensor of the last phalanx. The interossei of the foot agree on the whole with what has been observed in man and the chimpanzee, though there is a tendency to a division of the muscles, a slight approximation to the arrangement in the hand. The dorsal interosseous muscle of the second and fourth spaces presents the great peculiarity of being divided in the middle line into two distinct muscles, each having a tendon inserted into the opposed sides of the fingers bounding the space. There is also a distinct "interosseus volaris primus," as in the hand of man. On the whole, the muscular arrangements of the limb leave us much in the same uncertainty as the osteology, in reference to the nearer approach to man, presented by the gorilla or chimpanzee.

The larynx in its general characters resembles that of man and the chimpanzee. Connected with it in the adult gorilla is a system of great cavities, developments of the two laryngeal sacculi, each of which is equally dilated, and produced into large cæcal sacculated pouches, extending all over the sides of the neck in the interspaces between the muscles, from the rami of the lower jaw to the axillæ. As age advances the sacs of the two sides coalesce in the middle line over the trachea, and form an elongated bag, the upper end of which fits into the hollow of the body of the hyoid bone. The use of this immense and complex apparatus is not known.

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Anatomy of the Gorilla continued.–Of the structure of the internal organs of the gorilla, very little is known. Duvernoy has described the larynx and male organs of generation; Gratiolet the brain, from an exceedingly imperfect specimen; and Professor Huxley has himself been able to add some observations upon the thoracic and abdominal viscera. The heart is very human in form and the great arteries spring from the arch of the aorta in precisely the same manner as in man,–that is, the right carotid and subclavian arise from a common innominate vessel, and the left carotid and left subclavian separately from the aorta,–an arrangement which is soon lost in descending the series of apes. The lungs are divided into the same number of lobes as in man. The stomach is of the same form, and the cæcum very large, and provided with a long vermiform appendix. The liver in the only specimen examined departs remarkably from the human type, inasmuch as both right and left lobes are subdivided by deep fissures. The state of the brain examined by Gratiolet only sufficed to show that the principal sulci and gyri agreed with those of the chimpanzee. The form of the organ is, however, well seen in a cast of the interior of the cranium. It is longer and more depressed than in the chimpanzee, and the olfactory lobes are more prominent. When the tentorial plane is horizontal, the posterior lobes of the cerebrum project to a marked extent beyond the cerebellum. The glans penis is more developed than in the chimpanzee, having a button-shaped dilatation at the extremity.

The female gorilla is much smaller than the male. Her skull wants the great crests or ridges, and her teeth, especially the canines, are smaller. The pelvis of the female presents a considerable approximation to the form of the human pelvis. It is much shorter than in the male, somewhat narrower from spine to spine of the ilium, and while the transverse diameter of the brim is nearly equal in the two sexes, the antero-posterior diameter is very much less in the female. In the outlet of the pelvis the distinction between the sexes is not so marked. As far as could be learned from measurements of two young gorillas, the law of growth is the same as in the chimpanzee.

Professor Huxley here took occasion to revert to the chimpanzee, for the purpose of describing the placenta and fœtus of one of these animals preserved in the College museum. The placenta was a circular mass, three inches and a-half in diameter, and half an inch thick, not divided into lobes. In its structure, as well as in the cord and membranes, it generally resembled the human placenta. The fœtus was eleven inches and a-half long, and would probably correspond to a human fœtus of the eighth month. As might be expected, the head was considerably larger in proportion to the rest of the body than in the adult or young after birth; the arms were notably shorter, which might at first be supposed to indicate an approximation to the human type, but the legs were also shorter to a proportionate amount. This shortening of the limbs is, then, a fœtal character, and as it had taken place to a corresponding extent in both limbs, it shows, in an interesting manner, the ape character of the chimpanzee strongly and definitely marked at this period of intra-uterine life.

The next animal taken under consideration was the orangoutang. It is only known to exist at present in the great islands of Borneo and Sumatra, where it is comparatively rare, and confines itself to the wooded, hilly, inland parts. There is no trustworthy evidence that it ever exceeds four feet four inches in height. The span is nearly twice th