« PreviousContinue »
into the base of the first instead of the terminal phalanx ; the fourth or short extensor is a new foot muscle, and unrepresented in either the hand or foot of man. Thus, in the peroneal region, and in that of the extensor, we find all the corresponding human muscles represented; moreover, there are certain modifications of arrangement, and a new muscle for the first digit introduced, to give more freedom and variety of movement in extension to that member. This muscle is a foot muscle, not a hand one; the divided tibialis anticus is rather a foot than a hand arrangement. There are no hand muscles introduced, though the great toe has four, and the thumb three extensors. There is here a great toe, more moveable in extension than any thumb.
We now turn to the sole of the foot. The three superficial muscles, the abductor pollicis, the flexor brevis digit., and the abductor minimi and digitorum are, as in the human sole, the first to come into view. On detaching the two last from the heel bone, we find, towards the outer border of the foot, a flexor brevis minimi digiti, and in the middle region the lumbricales and the tendons of the long and short flexors of the toes, with a small muscle accessory to the lumbricales arising from the long flexor tendon before its division. No muscular accessories arising from the os calcis and attached to the long flexor tendon were observed. At the outer border of the foot, when we abduct strongly the great toe, which can thus be brought to nearly a right angle with the rest of the foot, we see, after a little dissection, the abductor pollicis as a short doubly reuniform muscle, extending from the heel to the base of the first phalanx of the great toe, occupying considerable space, and close to it lie the two halves of the flexor brevis pollicis, separated by the tendon of the flexor longus pollicis. Lastly, between the great toe and the second is clearly to be observed the abductor pollicis. All these muscles of the great toe are highly developed and of great power; and, if they all act together, will very forcibly pull the great toe towards the middle of the sole of the foot; if the flexors of the other toes are made to act at the same time, the result will be a strong, rather oblique opposition of the great toe to the other four toes; and if an object like the branch of a tree be placed in the sole, it will be grasped with much firmness. There remains, however, to be noticed an interesting arrangement by which that action will be enforced and made more secure. It is this: the muscle called flexor longus pollicis is largely developed in the leg, extending down to the inner ankle, and ends in a strong tendon, which runs into the sole of the foot close to the os calcis, and apart, as in man, from the other tendons, opposito
to the foot of the great toe, it divides into two slips; one, the lesser, runs outwards at a certain angle, being confined at first under a strong ligament, as under a pulley, to the great toe, as its long flexor tendon ; the other, the larger division of the tendon, passes straight onward to the other toes, supplying each with an additional tendon. It will be obvious to any one inspecting sketch E, that when this muscle (therein named flexor digitorum et pollicis) is put in action, it will necessarily draw the great toe and the other four toes together, and that simultaneously, towards the middle of the sole. This addition of a fourth set of flexor tendons for the four outer toes, and with it a distinct provision for the simultaneous action of those toes with the first, is very remarkable, and seems to complete the foot of the chimpanzee as a perfect instrument of prehension. The absence of the human flexor accessorius may be presumed to be an advantage, as it provides more space in the sole for the object grasped, and as no transversus pedis was found, the distal ends of the metatarsals are left more free to separate and enlarge the grasp. Next to the surface of the bones was beautifully seen the tendon of the peroneus longus muscle, resuming, in its bony and ligamentous groove to its destination, the base of the metatarsal bone of the great toe. When we consider, then, this elaborate mechanism, and see that the opening of the foot is most carefully provided for by the existence in connection with the four outer toes of a short and a long extensor for each, and by the presence of four distinct extensors for the great toe alone; and observe that flexion or prehension is made certain, exact, and powerful, by the arrangement of flexors for each of the four outer toes, vigorous short muscles of the great toe, and a necessarily synchronous action of the great toe and the other four, we cannot avoid the conclusion that we have examined the most admirable prehensile organ adapted to arboreal life that we can imagine; we must also feel persuaded that the hinder limb of the chimpanzee is still a foot, a prehensile foot of high perfection, surpassing even the hand itself in firmness and precision of grasp, but not a hand.
The additions to the ordinary mechanism of the human foot that have here been noticed, are not, so to speak, borrowed from the hand, but are either extensions of the plan of the foot, or new parts that occur neither in the hands nor in the foot of man.
The function of prehension by the foot, as is well known, is one enjoyed, not only by apes and monkeys, but by many other animals; the parrots, cockatoos, and other birds, and the chameleon, to cite familiar examples, have prehensile feet; it is attached to the nasal organ in the tapirs and elephants, to the lips in the giraffes, horses, etc., and to the opposite or caudal end of the spine in certain monkeys and marsupials. Prehension, therefore, cannot be taken in the characteristic function of the hand of the higher animals.
Digestive Organs. The tongue, broad, fleshy, soft, and delicate, much resembled the tongue of a child. The milk-teeth, twenty in number, somewhat blackened, were all present. The total length of the alimentary canal was 15 feet 10 inches, or about six and a half times the length of the body. It is thus made up, viz.
- 0 3
0 6 Length of stomach along greater curve
0 colon, ascending, transverse, & descending 1 4 sigmoid curve
0 7 rectum
15 10 Outlines of the stomach and cæcum accompany the paper. The æsophagus is somewhat narrow; the stomach is shorter and more globular than in man; the left end, or cul de sac, well defined ; the pyloric extremity, funnel-shaped and abruptly bent back towards the cardia, which it nearly touches, is slightly marked off at the bend by a constriction, and there are two other smaller constrictions between this part and the duodenum. The drawing of the caput cæcum coli does not require particular notice. The peritoneum appears to be disposed very
much on the human model, the foramen of Winslow, for instance, and the bag behind the stomach, were quite human.
The liver, with the gall-bladder, all the parts at the transverse fissure being cut close off, weighed 10} ozs. Its vessels and membranes resembled those of a child. It is divided into two great lobes, right and left, and each of these has a small rather detached lobule situated behind the transverse fissure, and bordering on the fissure of the vena cava. The spleen is rather thin, longish, and notched on its anterior border. The suprarenal glands are long and of a yellow colour, contrasting with the kidneys, which are brown, and also unlobulated.
Skull and Brain. The vault of the cranium having been removed, casts in plaster were at once taken by Mr. John Hancock of the inner surface of the bone of the brain covered by the dura mater, and, after
the brain was removed, of the cerebral surface of the base of the skull. Thus a correct cast of the whole cerebral surface was secured. Before the brain was in any way disturbed from its natural position, the relation of the posterior lobes of the cerebrum to the cerebellum was carefully observed; and the ten persons present, anatomists and naturalists, were unanimous in declaring that the former projected backwards over the latter a quarter of an inch. In the removal of the brain, the disposition of the membrane and nerves was observed to be strikingly similar to the corresponding human parts. The arterial circle of Willis was quite human. The entire encephalon with arachnoid and pia mater, vessels and nerves attached, and as much of the spinal cord as could well be reached by an ordinary scalpel, was carefully removed, and its weight was found to be 13 ozs. and 6 drachms, which is to the weight of the whole body nearly as 1 is to 19. The vessels having been removed, and the membranes, the whole brain was put at once into spirits for preservation and hardening, so that the separate weights of cerebrum and cerebellum were not taken. The three great lobes of each cerebral hemisphere were seen well developed; the two anterior lobes formed together a blunt projection forwards, whilst beneath their inner borders projected as ridges downwards, the under surface of these lobes were distinctly concave; the middle lobes were more prominent downwards than in man, and the projection of the posterior lobes backwards, overlapping the cerebellum, appeared as decided as before. After the brain had been for three days in spirits, the cerebral hemispheres measured in length 4; ins., in breadth across the middle or widest part 31 ins., the greatest width of the cerebellar hemispheres being 2; ins.; so that the cerebellum is markedly overlapped laterally as well as pos. teriorly by the posterior lobes of the cerebrum. The convolutions of the cerebral hemispheres were numerous, somewhat intricate, and partially symmetrical, two main sulci, traceable one from the Sylvian issure, the other from the base at the back of the crura cerebri, appeared to mark out even on the top of the hemispheres the division nto anterior, middle, and posterior lobes, or masses of convolutions. The island of Reil in the fissure of Sylvius was quite evident with hree small convolutions. The corpus callosum, 14 in. in the length, showed as in man distinct though minute transverse striations, and a ongitudinal raphe formed of two slightly raised lines and an interjening groove. A section of the right hemisphere, to expose the ateral ventricle, showed as bold and as numerous projections of the xternal sulci into the white centrum ovale as are commonly seen in the human cerebrum. The ventricle itself was beautifully distinct, its anterior cornu curving boldly outwards in front of the striated body, its middle cornu winding outwards and downwards to the very bottom of the large middle lobe, and containing the hippocampus major and the corpus fimbriatus, and the choroid plexus and its posterior cornu extending in an ample curve backwards and inwards, so as almost to touch the grey matter of the surface next the median line, and having within it the projection called hippocampus minor, which may
still be seen. On the floor of the body of the ventricle are to be seen the corpora striata, the tæniæ semicirculares and the free edge of the fornix with the choroid plexus; these last lie on the velum interpositum, which covers the third ventricle and the optic thalami, quite as in man. Further investigation in this direction was forborne, as it was thought desirable to preserve, for the present occasion, the parts already enumerated. The fourth ventricle, as it is called, and its walls, as they could be examined without injuring those parts, were inspected; the cavity was closed behind, and had its small choroid plexus after the human pattern; a second similar, but smaller, plexus existed on each side, just outside of the ventricle, and attached to the cerebellum. The point of the calamus scriptorius was well defined, but no white lines of origin of the auditory nerve were distinguished; on the other side of the medulla oblongata, the usual nerves were met with, and the pyramids and olivary bodies clearly to be seen, but they were not further examined.
The cerebellum was laminated, and had the great human divisions ; on examining that part which overhangs the medulla oblongata, the inferior vermiform process, the uvula and tonsils, the flocculus, and other parts enumerated in human anatomy, could, without difficulty, be dissected out; the superior vermiform process, also, was evident on raising up carefully the posterior lobes of the brain.
The conclusions arrived at in this short and imperfect investigation are, it will easily be seen, those which have already and for some time past been made public by Professor Huxley, viz. : 1, that the chimpanzee is not, properly speaking, quadrumanous, but that it possesses four prehensile extremities, two hands, namely, and two feet; and 2, that the brain of the chimpanzee differs from the brain of the man only in size and weight, therefore in the smaller size and extent of its cerebral convolutions; the same parts, without exception, exist in both brains. Whether the cerebral matter of the ape differs from that of man in microscopic characters, or how otherwise it may differ, are problems yet to be worked out.