Chapter III (3)

It is important to remark that platycnemy has been regarded as a pithecoid structure, and for this reason the attempt has been made to establish the degraded position of those peoples which are most remarkable for platycnemy. But, as Boyd-Dawkins has already observed, although the tibiæ of the gorilla and the chimpanzee are to some extent platycnemic, they are much less so than the platycnemic bones of the human skeleton. The tibia of a male gorilla in the College of Surgeons Museum has an index width of 68·1, that of a female of 65·0, while the index of the chimpanzee’s tibia is 61·1, which is about the average of the tibias of Perthichwareu. It is unnecessary to indicate the other marked distinctions between the tibiæ of men and apes; if platycnemy is to be regarded as genetic, it must be admitted that man has in this particular far exceeded apes.[57] Neither the gorilla, the chimpanzee, the orang-utan, nor even the baboon possesses a tibia which is flattened in its upper or middle part. In all these apes the middle of the bone is more or less rounded, almost as if it had been rounded by a turning-lathe. According to my experience, the degree of platycnemy in anthropoids is subject to certain variations. It appears to me to be least marked in the aged male gorilla (Fig. 41), and in the gibbon (_Hylobates agilis_, _syndactylus_), in which latter animal the transverse section of the tibia represents an almost equilateral triangle. The platycnemy was more marked in an almost adult female gorilla, still more decided in an aged male chimpanzee, which came from the river Kiulu, and again in an aged female chimpanzee. On the other hand, the centre of the shaft of the tibia in another aged male chimpanzee which came from Loango, was rounded, and not platycnemic. In the tibia of an adult orang-utan which I examined, the platycnemy was very marked. But I agree with Boyd-Dawkins in never having met with an anthropoid in which the platycnemy is so considerable as it is, for instance, in the Cro-Magnon tibia, and in another found at Troy.

Fig. 46.--Skeleton of the human foot, seen from above. _a_,
Astragalus. _b_, Os calcis. _c_, Scaphoid bone. _d_, _e_, _f_,
Cuneiform bones. _g_, Cuboid bone. _h_, Metatarsal bones. _ii_,
Phalanges.
]

If we give a cursory glance at the lower limbs of apes, we see that all the same characteristics are present in their tarsus that we find in the human tarsus. In each case there is an astragalus, an _os calcis_, a scaphoid bone, three cuneiform bones, and a cuboid bone. There are undoubtedly several peculiarities in which the tarsus differs from the corresponding part of the human foot. The first metatarsal bone is joined to the first cuneiform bone by an articular facet which extends from the back to the sole of the foot. This joint plays a part resembling that of the thumb of the human hand (see Figs. 20 and 46).

In Huxley’s opinion, the hinder limbs of the gorilla terminate in a true foot, with a very movable great toe. It is undoubtedly a prehensile foot, but in no sense a hand. It is a foot which does not differ from the human foot in any essential characteristics, but only in relative circumstances, in the degree of flexibility, and in the subordinate arrangements of its parts. Huxley adds that it must not be supposed that he wishes to undervalue differences which, however, he does not regard as fundamental. They are important enough of their kind, since in any case the structure of the foot is in close correlation with the other parts of the organism. Although it cannot be doubted that the increased division of labour in man, which relegates the function of support entirely to the legs and feet, is a significant advance in structure; yet, regarded as a whole from the anatomical point of view, the points of agreement between the human foot and that of the gorilla are much more striking and significant than their differences.

The differences in the foot of the orang are still greater; in the very long toes and short tarsus, the short great toe and the removal of the heel from the ground, in the great obliquity of the joints which connect the foot with the shank-bones, and in the absence of a long flexor muscle to move the great toe, the orang’s foot differs still more from that of the gorilla than the latter differs from the human foot. In some of the lower apes the hands and feet are still further removed from those of the gorilla than in the case of the orang. In the American apes the thumb can no longer be opposed; in the ateles it is reduced to a mere rudiment, covered with skin; in the sahius it is bent forwards and provided with a curved claw like the other fingers. In all these cases there is no doubt that the hand differs more from that of the gorilla than the gorilla’s hand differs from that of man.[58]

Flower remarks that the chief distinction between the foot of a man and an ape consists in the fact that the latter is transformed into a prehensile organ. The tarsal and metatarsal bones, and the phalanges are of the same number in both orders, and in the same relative position, only in the foot of the ape the facet for articulation of the first cuneiform bone with the great toe is saddle-shaped, and obliquely directed towards the inner or tibial side of the foot. Thus, the great toe is separated from the others, and so placed, that when it is bent, it is directed downwards towards the sole, and is opposed to the other toes, much more opposed to them than is the case with the thumb of the human hand.[59] Owen also speaks of the characteristic transformation of the great toe of an ape’s foot into a thumb, opposed to the other toes, and adapted for grasping.[60]

K. E. von Bär does not agree with Huxley in considering that there is less difference between man and the gorilla than that which exists between different species of apes. “There are,” Von Bär remarks, “differences of various kinds among apes. In some the thumb is only a stump; in others, as in the orang-utan, the fingers of the hinder extremities are so long and curved that they cannot be extended on flat ground; in many of the smaller apes this member is still more like a hand than in the larger species, and the fingers can be easily spread out on the ground. In this case the foot is of a much blunter form, and is more flexible, so that the sole, which is properly turned inward, can lie flat on the ground. The heavier the body of the animal, the more sharply cut the structure of the foot must be, so that it does not admit of the free movements which are possible in the hand. But all these are only modifications of a climbing foot, or prehensile member--that is, of a hand, not modifications of a foot resting firmly on the ground and supporting the whole weight of the body.

“It must not be forgotten that the structure of the skeleton is subject to mechanical laws, which may be traced through the whole series of the animal world. This is readily apparent when we turn to the human structure.

“The human foot rests for the greater part of its length on the ground, that is to say, with the heel and centre of the foot, which form together a firm arch. The tarsus consists of the astragalus, and also of the _os calcis_, which in man form a very prominent part, taking a backward and downward direction, and of five other bones. The metatarsus consists of five bones, on which the five toes are inserted. In man these metatarsal bones are considerably longer than the separate phalanges. Thus, the arch on which man is supported in an erect position extends from the heel to the extremities of the metatarsal bones. The several bones are slightly movable, but they are so firmly connected that they can diverge but little from each other, unless muscular power is exerted. In order to press the toes upon the ground, it is again necessary to exert the muscles. The arched instep has this advantage, that the foot can take a better hold of the slight inequalities of the ground. In a profile view of the skeleton of a human foot, the shortness of the toes, in comparison with the length of the arched instep, is very apparent. In any natural position, even when man is not walking or standing, the sole of the foot is not turned inwards, but downwards.... The toes of the gorilla take the form of a hand, since the great toe stands separate like a thumb, while the other toes are turned outwards. In the gorilla the tarsus is short, and the heel is bent inwards. The several bones of the human foot are undoubtedly present in the hind hand of a gorilla, but the organ is changed into a prehensile organ or hand. The conditions are the same as in the parts of the mouth in insects which in some cases form movable mandibles, while in others they are attenuated into a proboscis. When it is asserted that apes are not quadrumanous, it is as if we were to say that flies have no proboscis, but attenuated mandibles.”[61]

All apes, including anthropoids, occasionally make use of their hinder extremities in order to snatch at objects. They also grasp with them in climbing. On such occasions, when they wish to secure the fruit they have seized from the voracity of their fellows, they take it between the toes of one hinder extremity, in order to be able to get away more quickly by means of the other, and by the use of both hands.

From what we have said, it will be seen how difficult it is to reconcile the views of different observers with respect to the fitting term to be given to the hinder extremities of apes. Against those who uphold the designation of _hind hands_ we must oppose the anatomical structure, and also the fact that a true hand ought to possess the power of rotation in a degree which exists in the fore, but not in the hind, extremities of apes. On this account I have already adopted, as more suitable and equally distinctive, the term of _prehensile foot_ for this member.[62] I agree with Haeckel in rejecting the common designation of apes as four-handed or quadrumanous.

The bands or ligaments which connect the different parts of the anthropoid skeleton together, and convert the detached elements into a movable machinery, do not on the whole differ much from the same structure in man. A detailed account of these ligaments would, for several reasons, be out of place in this work, and I shall only mention a few special and more interesting distinctions. Such, for example, is the uncommon strength of the _ligamentum nuchæ_ in the gorilla, which is quite in harmony with the great development of the spinous processes of the upper cervical vertebræ, and with the flattening of the squamous occipital portion. Since the sacral vertebræ are deeply inserted between the high ilia, the ilio-lumbar ligaments (_ligamenta iliolumbalia_) and the sacro-iliac ligaments (_ligamenta iliosacralia_) are of considerable size. In agreement with the projection in a downward direction of the high, narrow ischial bones, the sacro-sciatic ligaments which extend between these and the sacrum are very long in the chimpanzee. Although in this case the ischial spine is only represented by a roughness of the bone, yet there is on either side between this and the sacrum a powerful lesser sacro-sciatic ligament (_ligamentum spinoso-sacrum_).

The well-known anatomist, J. F. Meckel, has asserted that the depression in the head of the femur (_fovea capitis_), which serves for the insertion of the round ligament (_ligamentum teres_), is absent in the chimpanzee and orang, and he adds that it is also absent in the gibbon. In a skeleton of a young chimpanzee which had not shed its milk-teeth, and of which the ligaments were also preserved, Welcker found a fully developed round ligament inserted almost in the centre of the head of the femur. This agrees in every particular with the same formation in man. On the other hand, no trace of a round ligament was to be found in the hip-joint of a young orang-utan. The cartilaginous envelope of the head of the femur was smooth throughout, without any indication of a place for inserting the ligament. Welcker again found no such depression in the femur of an aged male orang-utan, nor was there any trace of it in another aged male orang, designated as _Simia Morio_. Welcker believes that he has established the fact that the round ligament is wanting in the orang-utan, but that it is present in the gorilla, chimpanzee, and gibbon. The same naturalist remarks that, although we may certainly assume that the round ligament is absent wherever there is no depression in the head of the femur, yet the existence of such a depression in the acetabulum (_fovea acetabuli_) is not enough to prove that a round ligament was inserted in it. The innominate bones of an adult orang-utan were examined by Welcker, and displayed a small, but well-defined depression, as if destined for a receptacle for this ligament,[63] running from the cotyloid notch down to the bottom of the acetabulum, between the two horns of the semilunar-shaped articular cartilage.

In a subsequent paper, Welcker states that the absence of the round ligament in the orang-utan, and its presence in the chimpanzee, had been previously established by Camper and Owen.[64] In three specimens of orangs which he had obtained immediately after death, Owen found that the round ligament was imperfectly developed on both sides. The chimpanzee differs from the orang in possessing a depression on the head of the femur. In the gorilla, as Owen observes, this depression has almost the same depth and relative position as in man. At Welcker’s request, Professor Dippel ascertained the presence of the depression in the femur of a gorilla skeleton which is preserved in the natural history collection at Darmstadt. St. George Mivart saw the skeleton of an orang in which the femur was marked with a slight but plainly indicated depression, just where the round ligament is usually attached. Welcker thinks it probable that in some specimens of the gorilla the round ligament is only slightly developed, and that in others it is altogether wanting. On several femurs of gorillas, this naturalist observed only doubtful traces of the depression in question. Duvernoy found the round ligament fully developed in the gorilla and chimpanzee. Vrolik failed to find it in the orang-utan, but ascertained its presence in the chimpanzee. Gratiolet and Alix saw that it was fully developed in _Troglodytes Aubryi_.

In addition to these somewhat conflicting assertions, I have myself observed, in the gorilla innominate and femur bones examined by me, more or less distinct indications of the depression which receives the round ligament. The ligament itself has been preserved with the body of a gorilla. The same remark applies to the skeletons and bodies of chimpanzees. In the case of the skeleton of an orang, slight indications of a depression were observed on the head of the left femur, and these indications were absent in the femurs of other specimens. In a large orang-utan which died in the Berlin Aquarium, only short, filamentous tufts of streaky fibres were apparent in the right acetabulum, and these were intermingled singly or in groups with the cartilaginous cells, somewhat resembling the cartilaginous corpuscles of the synovial membrane. From these facts we may conclude that the round ligament is generally but not invariably present in the gorilla and chimpanzee, and that it is altogether absent in the orang-utan. In the gibbon it is present in the majority of cases. I have myself observed it in _Hylobates agilis_, _leuciscus_, and _syndactylus_. Owen asserts that the unsteady gait of the orang is partly due to the absence of this ligament, but the truth of this surmise is rendered doubtful by the fact that the ligament is not unfrequently absent in other anthropoids. Moreover, the gait of all these arboreal and climbing animals is extremely ungainly.

The muscular system of anthropoid apes is very interesting. I must necessarily refrain from giving a detailed account of it, and will only mention some points in connection with this organic system, and their relation to corresponding points in the muscular system of man. I rely partly on the researches of others, and partly on my own. The amount of material which has been collected up to this time is, unfortunately, too scanty to enable us to draw satisfactory conclusions in all cases. We are often unable to decide whether the conditions presented to us in the case of anthropoids are normal or exceptional. Nor are the statistics of muscular variations in the human subject by any means firmly established. My own labours in this direction are not yet concluded. The assertions on the subject which have been published to the world and accepted as authoritative have already been shown to be to some extent untrustworthy. Even the little which I am now able to produce may not altogether stand the test of subsequent research. Brühl justly remarks that in no department of anatomy more than in that which treats of the muscles, is it more essential that we should not decide whether a form is normal or exceptional until it has been repeatedly examined.[65]

Fig. 48.--Muscles of the head and face of a European. 1,
1′, Occipito-frontalis. 2, 3, Orbicularis palpebrarum. 4,
Pyramidalis nasi. 5, Levator labii superioris alæque nasi. 6,
Compressor naris. 7, Levator labii superioris. 7′, Zygomaticus
minor. 8, Levator anguli oris. 8′, Zygomaticus major. 9,
Orbicularis oris. 9′, Levator menti. 9″, Depressor labii
inferioris. 10, Depressor anguli oris. 11, Masseter. 12,
13, Risorius and the buccinator by which it is covered. 15,
Trapezius. 16, Attrahens. 17, 19, Attollens. 20, Retrahens
aurem. 21, Sterno-mastoid. 22, Splenius. A. Tendinous
aponeurosis. C. Malar bone (the parotis is removed). F. Skin of
neck.
]

The cranial muscles of anthropoids are formed like those of men, except in a few unimportant particulars (comp. Figs. 48 and 50). I have not observed in anthropoids the muscular fibres which in man branch out from the orbicular muscle of the eye, and overlap the cheeks and temples, and which are considerably developed in the head of a Monjalo negro which was dissected by me (Fig. 49, ~3~, ~3′~). In apes that portion of the orbicular muscle which covers the supra-orbital ridge is very marked. There is generally a considerable layer of muscle on the nose and upper lip. I have dissected it in detail in anthropoid and other apes, including those of America; _i.e._ the zygomatic muscles, the levator labii superioris, and the levator labii superioris alæque nasi. This has also been done by Duvernoy, Alix, and Gratiolet, in the case of anthropoids dissected by them, as well as by Macalister and Bischoff.

Fig. 49.--Head-muscles of a Monjalese negro. 1, 2,
Occipito-frontalis. 3, 3′, Orbicularis palpebrarum. 4,
Pyramidalis nasi. 4′, Levator labii superioris. 6, Levator
labii superioris alæque nasi. 6′, Compressor naris. 7′, Levator
anguli oris. 8, 8′, Zygomatici major et minor. 9, Orbicularis
oris. 9′, Levator menti. 9″, Depressor labii inferioris. 9‴,
Depressor anguli oris. 11, Masseter. 13, Buccinator. 14,
Platysma. 15, Trapezius. 17, 18, Attollens and attrahens
aurem. 19, Embedded temporal muscle. 20, Retrahens aurem. 21,
Sterno-mastoid. 22, Deeply set muscles of neck. A, Tendinous
aponeurosis. C, Zygoma. E, Parotis. *, Stensonian duct.
]

Bischoff was only able to identify a wide zygomatic muscle in the orang with the small zygomatic in man. In the orang, the gibbon, and the baboon, as well as in _Innus sinicus_ and _Ateles_, I myself was quite able to trace a division into a large and small zygomatic. In the gorilla dissected by me the levator labii superioris alæque nasi was very wide (Fig. 50, ~6~). In the case of a gorilla, Ehlers dissected the small zygomatic muscle, together with the levator labii superioris alæque nasi, in the manner introduced by Henle as a single square muscle of the upper lip (_Musculus quadratus labii superioris_). In the gorilla I observed a levator alæque nasi, together with the already mentioned levator labii superioris; but I failed to find any separate levator labii superioris. The very wide cartilage of the nose is occupied by a considerable amount of muscular tissue. All these muscles are present in the orang, but they are of small size and separated into detached bundles. The pyramidalis nasi may be traced in every instance, especially in the gorilla (Fig. 50, ~4~) and in the orang. It is not so strongly developed in the chimpanzee and gibbon, but is not absent in these apes, nor in those which are not anthropoid, such as the baboon, and ateles, or climbing ape.

Fig. 50.--Head-muscles of gorilla presented in Fig. 3. 1,
2, Occipito-frontalis. 3, 3′, Orbicularis palpebrarum. 4,
Pyramidalis nasi. 5, Levator alæ nasi. 6, Levator labii
superioris alæque nasi. 7, Zygomaticus minor. 7′, Levator
anguli oris. 8, Zygomaticus major. 9, 9′, Orbicularis oris.
10, Risorius. 11, 16, Masseter. 1′, Buccinator. 12, Depressor
anguli oris. 13, Buccinator. 14, Platysma. 15, Trapezius. 17,
Temporal. 18, 19, 20, Attrahens, attollens, and retrahens
aurem. 21, Lesser muscle of helix. A, Tendinous aponeurosis. B,
Cartilage of nostril. C, Zygoma. D, External ear. *, Stensonian
duct.
]

I myself follow the original division of the muscles into those which belong to the nostril and upper lip, in accordance with the principles of Duchenne, Darwin, Gamba,[66] and others, and I do so the more readily, since it is impossible not to perceive the manifold and lively mimetic action which takes place in this particular region of an ape’s head. The distinct action of the levator labii superioris alæque nasi, the dilation of the nostrils, the function of a strongly developed levator anguli oris, are especially characteristic of the gorilla; but they are also perceptible in the chimpanzee and gibbon. The orang’s face is the least mobile. I observed that in the gorilla the risorius was very long, branching slightly in the fore-part of the corner of the mouth, and behind into three distinct wide bundles. The lowest bundle covered the platysma myoides, but could not be regarded as part of the latter. In one chimpanzee I found that the risorius was slightly developed, and in other animals of that species I failed to trace it at all. Alix and Gratiolet represent the Aubry chimpanzee (Plate ix. Fig. 1, ~15~) with the risorius strongly developed. I have not observed this formation either in the orang or the gibbon, but it was apparent in one of the ateles (_Ateles leucophthalmos_). In this case the muscle covered the platysma myoides and Stenson’s duct, _i.e._ the duct leading out of the parotid gland (Fig. 50, *).

For some time I was disposed to regard the risorius of this ape as only a radiation of the platysma myoides, but my opinion upon this point is again shaken.

In the gorilla a faint depressor anguli oris and an equally faint depressor labii inferioris may be observed, the latter partly covered by the large and predominant orbicularis oris (Fig. 50). In the chimpanzee the two depressors are plainly apparent, and in the gibbon the one first named was at any rate developed. The platysma myoides, the depressors just mentioned, and the crescent-shaped orbiculares are in this animal in close connection with each other. Froriep’s suggestion becomes ever more probable, that these muscles of the lower lip owe their origin to the intersection of the opposite portions of the skin-muscles of the neck which overlap the face. The buccinator muscle in anthropoids resembles on the whole that of man, and in both cases is pierced by Stenson’s duct (Fig. 50). The form of the masseter muscle is common to both (see Fig. 50, ~11, 16~). In the external ear of anthropoids there is an attrahens, attollens, retrahens (Fig. 50). Compared with that of a white man, and still more with that of a negro (see Figs. 48, ~19~, and 49, ~17~), the attollens is only slightly developed. The muscles attached to the cartilages of the ear are extremely scanty or partially wanting, which is also sometimes the case with man. The muscles of the helix are most strongly marked in the gorilla (see, for example, Fig. 50, ~21~). Tiedemann, Bischoff’s brother-in-law, carefully observed two living chimpanzees in Philadelphia for six months without detecting any movement of the ears. My own observation confirms his assertion and the remarks of Darwin, which I have already quoted, to the effect that anthropoids are incapable of moving their ears. I know of no individual exceptions. This is the more remarkable since some men have retained the power of voluntarily moving their ears, and the same power is also found in some species of apes, such as the sea-cats, baboons, macacas, and magots.

It will not here be out of place to say something of the characteristics, previously mentioned, of the physiognomical expression of anthropoid apes. Thus, for example, when the gorilla is agitated, he can move the skin of his head and bristle the hair which covers this region. The chimpanzee can also move the skin of the head, but with no very apparent bristling of the hair. The large male orang, which was in the Berlin Aquarium in 1876, bristled his hair and the skin of his head when he was much enraged. It is known that in some instances man also possesses this power.

I have already spoken of the expression of the eyes of these animals. I will only add that when anthropoids of every species are in great pain or seriously ill, the expression of their eyes is often most affecting.

The forehead of these animals is frequently marked by transverse furrows, and especially, as Darwin justly observes, when they raise their eyebrows. The same great observer considers that the countenances of anthropoids are, in comparison with those of men, generally inexpressive, and indeed, chiefly in consequence of the fact that they do not wrinkle the forehead when they are excited. The wrinkling of the forehead, which is one of the most significant forms of expression in man, is due to the action of the corrugatores supercilii, by which the eyebrows are drawn down and closer to each other, so as to form vertical folds on the forehead. It has been asserted that the orang and chimpanzee possess these muscles, but they seem to be rarely exercised--at any rate, to any remarkable extent.[67] When Darwin brought a chimpanzee out of his dark chamber into bright sunshine, he only once observed a slight wrinkling of the forehead. When the same observer tickled the nose of a chimpanzee with a straw, its face was slightly wrinkled, and faint vertical furrows appeared between the eyebrows.[68] Darwin never observed any wrinkling of the forehead in an orang. I myself have observed a contraction of that region of the brows which is covered with bristly hairs, and a wrinkling of the skin which covers the bridge of the nose in the gorilla and the chimpanzee, and have illustrated this expression by a drawing.

Darwin goes on to say that when a young chimpanzee is tickled, to which, as in the case of children, their armpits are peculiarly sensitive, he generally utters a chuckling or laughing sound, although sometimes the laugh is silent. The corners of the mouth are then drawn back, and this sometimes causes the eyelids to be slightly wrinkled. This wrinkling, which is so characteristic of the human laugh, is still more apparent in some of the other apes. In the chimpanzee the teeth of the upper jaw are not exposed when he utters this laughing sound, and in this respect he differs from man. Darwin further observes that when the tickled young orang ceases to laugh, an expression passes over his face, which, according to Wallace, may be called a smile. Darwin has observed something similar in the chimpanzee.[69]

My own observation confirms what has been said of the chuckling of a tickled chimpanzee. When Dr. Hermes, the director of the Berlin Aquarium, played with the chimpanzee which was kept in that establishment, a contortion of the corner of the mouth, resembling a somewhat sardonic smile, at once appeared. No specimen displayed this smile with so much effect as the lively Augustus, who delighted visitors by his inexhaustible humour in 1879. The gorilla, of which an illustration is given in Fig. 3, also drew down the corner of his mouth when he was pleased, by means of the muscular system which we have just described.

When the gorilla is provoked, he displays both rows of teeth, and opens his mouth to utter sounds of fury, while making ready to fight. It is well known that anthropoids are able to pout and project their lips; and Darwin says that they do this, not only when they are slightly teased, and are sullen or disappointed, but also when anything occurs to make them uneasy.

I have often observed in chimpanzees a slight wrinkling of the region of the nasal cartilage, and even a vibration in a lateral and upward direction. In any case, the muscles which we have described as acting on the nose and upper lip are exercised.

The platysma myoides, which extends in man from the lower row of teeth to just below the clavicle, occupies about the same area in the gibbon and in other apes (Fig. 50). In the chimpanzee, however, this muscle extends as high as the zygomatic arch, or even higher. In the gorilla also I observed that this part extends comparatively high on the face. In chimpanzees, orangs, and gibbons the upper fibres of this muscle seem to form the risorius. In one case the platysma myoides sent forth a fasciculus, about 18 mm. in width, to the beginning of the lower temporal ridges. In the gorilla I saw that the uppermost fibres of the platysma myoides were partly covered by the risorius (Fig. 50, ~10~).

From the corresponding muscle in the orang the lower fibres tend far backward, and are in connection with the deltoid muscle covering a segment of the capsular ligament. This muscle wrinkles the skin of the neck, and helps to draw down the lower jaw. In cases in which it extends far in an upward direction, as in those we have cited, it affects the lateral extension of the middle and lower skin on the faces of these animals, as well as the grinning contortion of the corner of the mouth. It may also have to do with the grumbling sound issuing from the throat-pouch, which is uttered by the animal when agitated, as he rapidly opens and closes his mouth.

The strong sterno-cleido-mastoid muscle found in these animals, and especially in the orang and gibbon, can be divided without difficulty into a sternal and clavicular portion. The two portions diverge from each other in a downward direction. As Bischoff justly states, a muscle not hitherto observed in man may be traced in all four species of anthropoids, a muscle which extends from the external part of the clavicle to the transverse process of the first cervical vertebra. Bischoff has called it the musculus omocervicalis. It is found in other apes, although the site of its origin varies, sometimes occurring on the spine of the scapula. Our Munich anatomist differs from Huxley in regarding this muscle as “a brilliant proof of the relation of all apes with each other.” I give this assertion without further comment.

The muscles which extend between the head, sternum, and clavicle, together with the muscles of the acromion process of the scapula, make an external covering to the throat-pouch, which I shall describe presently. The pectoralis major of the gorilla, as well as that of man, divides into two portions, one attached to the clavicle, the other to the cartilages of the true ribs. The former is divided from the deltoid by a wide interval, filled with connective tissue and fat. But both portions of the pectoralis major are divided by a tolerably wide space, into which, in Bischoff’s opinion, the throat-pouch is inserted. This, however, I do not believe, since that organ would be compressed and strangulated between the two portions of muscle whenever they were exercised. It may, however, be supposed that room for an enlargement of the throat-pouch when the animal is bellowing is afforded by the existence of these spaces. Bischoff is right in the assertion that the clavicular portion of the pectoralis major is wanting in the orang-utan. The upper part of this muscle springs directly from the sternum. The lower sternal ribs give origin to the pectoralis minor. The chimpanzee and gibbon display clearly in this muscle the separation we have mentioned into a clavicular and a sternal portion.

The structure of the pectoralis minor in these apes is full of interest. In the gorilla it divides into an upper portion of firmer tissue, less easily separable into digitations, which arises from the third to the fifth ribs, and a lower portion, separable into three digitations, of which the upper segment laps considerably over the lower segment of the upper portion. In the chimpanzee an upper portion of less firm texture extends from the second to the fourth, and a lower with three digitations from the fourth to the seventh ribs. This second lower portion is sometimes absent. I have seen the upper portion attached to the coracoid process of the scapula, and the lower portion to the ridge of the greater tuberosity of the humerus. In the orang an upper portion, separable into three digitations, extends from the second to the fifth ribs, and is attached to the coracoid process. A lower portion, also separable into three digitations, extends from the fifth to the seventh ribs, and is also attached either to the greater tuberosity of the humerus or to its edge; this latter portion projects below over the pectoralis major. In the gibbon (_Hylobates albimanus_), the upper portion starts from the second, the lower from the third to the fifth ribs. It may here be remarked that the pectoralis minor is in man also sometimes separable into digitations, which may be connected both with the coracoid process and with the capsular ligament of the shoulder-joint. In anthropoids the tendon of insertion of this muscle is remarkably slender.

According to Duvernoy, in the gorilla a fibrous, hood-like fascia covers the whole region of the occiput and neck. In adult males this fascia is 20 mm. in thickness. In a female dissected by me the rudiments of a similar hood-like cervical fascia were present. Duvernoy is justified in supposing that this is not yet developed in the young gorilla, and that a layer of connective tissue and fat is substituted for it. In a young gorilla I saw the trapezius divided into distinct bundles of flesh by layers of fat (Fig. 50, ~15~). The fascia corresponds to the great development of the trapezius, and the same characteristic development exists in other anthropoids. The adult male gorilla displays a powerful _ligamentum nuchæ_ in connection with the long spinous processes of the cervical vertebræ, as well as powerful inter-spinales muscles, spinales colli, and semi-spinales colli and dorsi. The great development of the spinous processes of the dorsal vertebræ of gorillas (Fig. 17), and also chimpanzees and orangs, involve the development of powerful semi-spinales, as well as of strong, fourfold spinales and inter-spinales muscles. The whole of the fleshy formation of the neck of an adult male gorilla which is covered by the trapezius is very voluminous, and especially the splenius capitis and colli, the long cervical muscle (_Musculus longissimus cervicis_), and the long head-muscle (_Musculus longissimus capitis_), which have also been regarded by me as parts of the long spinal extensor, and finally the oblique and vertical muscles at the back of the head. With Chappuy, I am disposed to regard the latter as modifications of the spinales and inter-spinales.

The levator anguli scapulæ is divided in anthropoids as in man. The subclavius is slender, except in the gorilla, and in the latter animal it sends a tendon obliquely to the coracoid process.

In all anthropoids the deltoid is strongly developed. In the gorilla it projects forwards and outwards in order to attach itself to the humerus, almost in its centre. Here it is separated from the brachialis anticus in a manner with which we are only imperfectly acquainted. It extends nearly as far in the gibbon and orang, while in the chimpanzee its attachment is higher up. Bischoff observes, and it was previously suggested by Vrolik, that in the chimpanzee the coraco-brachialis muscle possesses at its origin a moderately large second portion, which tends downwards over the lesser tuberosity of the humerus, and adheres to its edge. But I have seen both portions of the muscle in question attached to the coracoid process of the scapula in apes of this species. In the gorilla, orang, and gibbon the position of this muscle corresponds to that in man.

Chapman and Bischoff speak of a muscle common to all apes which starts from the tendinous attachment of the _latissimus dorsi_ on the edge of the lesser tuberosity of the humerus, and tends downwards on the inner side of the humerus, and to this muscle they give the name _latissimo-condyloideus_. Bischoff goes on to say that this muscle goes in some cases into the fascia which covers the biceps; and in others, as in the baboon, it is attached to the inner inter-muscular septum and to the internal condyle of the humerus. In the gibbon it only extends as far as the centre of the humerus, but in the orang it reaches to the condyle, where it is pierced by the ulnar nerve. Bischoff adds that this formation is wanting in man.

This structure is indeed remarkable in anthropoids. The muscle starts in a lateral direction from the insertion point of the _latissimus dorsi_. In the gorilla alone I observed that it started from the coracoid process of the scapula, together with the two portions of the pectoralis minor; it was connected for a space with the coraco-brachialis, and finally it was attached, in the upper part of the lower third of the humerus, to the inter-muscular septum which is found between the brachialis anticus and the triceps. In the chimpanzee, on the other hand, it has its origin in the _latissimus dorsi_, and divides into an anterior and posterior portion; the former is attached to the inner condyle of the humerus, while the latter is connected either with the middle or inner head of the triceps. In the orang the same division of this muscle may occur. In one of these animals I observed an anterior portion, very thin and semi-membranous, attached by an extremely slight tendon to the coracoid process of the shoulder-blade, while the hind portion issued from the _latissimus dorsi_. They were both in connection with the triceps and brachialis anticus. In other instances the muscle consisted only of the posterior portion, issuing from the _latissimus dorsi_. In the white-handed gibbon, the muscle issued from the region in which the tendons of the _latissimus dorsi_ and of the teres major are united, and was inserted into the fascia which is found between the bicipital and the brachialis anterior. This attachment may also occur in the centre of the shaft of the humerus. Chapman and Chudzinsky have observed anomalous instances of this formation in coloured races.[70]

It is well known that in man the biceps is inserted into the tuberosity of the radius by means of a flattened round tendon. This tendon, however, opposite the bend of the elbow, gives off a broad expansion, which passes into the fascia of the forearm, and is termed _Aponeurosis bicipitis_. In the gorilla this aponeurosis is carried on as strong fibrous bundles of the fascia of the forearm into the palmar fascia. In the gibbon the short head of the muscle does not always start from the lesser tuberosity of the humerus, nor from the tendon of the pectoralis major (Huxley), but sometimes from the edge of the lesser tuberosity, which is here connected with the _latissimus dorsi_, as well as with the sub-scapularis, the brachialis anticus, which is more to the side, and with the triceps. In the gibbon, as Bischoff justly observes, the supinator longus only reaches as far as the centre of the radius, instead of extending to the styloid process of that bone, as it does in other anthropoids, and in man.

The palmaris longus is wanting in the gorilla, but not in other anthropoids. The long flexor muscles of the fingers and the lumbricales resemble those of man (Figs. 51, 52). The flexor longus pollicis is absent in the gorilla. Duvernoy considers that it is replaced by a tendon of the long flexor of the fore-finger, but I have been unable to verify the existence of this tendon. The same muscle is also absent in the chimpanzee and the orang, but it may be traced in _Hylobates albimanus_. Chapman states that in the gorilla the pronator radii teres only sends forth one head,[71] but I have found it to be bicipital in animals of this species. The lower or hinder head issues, as in man, from the coronoid process of the ulna. Both in the gorilla and in the chimpanzee it extends far in a downwards direction on the radius (Fig. 52). The flexor carpi radialis starts in the chimpanzee with one head from the inner condyle of the humerus, and with the other from the radius. Bischoff describes the structure of the long abductor of the thumb in the orang, the baboon, the _pithecia_, and the _hapale_ as resembling that of man. But in the gorilla, the chimpanzee, and the macaca the tendon divides into two parts. Nor does one tendon belong, as in man, to a short extensor of the thumb, but the latter is wholly absent, and the division of the tendon only implies a continued division of the attachment to the trapezium, as well as to the metacarpal bones of the thumb. This division of the tendon also occurs in the gorilla, which likewise possesses a short extensor of the thumb. In this point, again, apes display a greater likeness to one another than to man.

Fig. 51.--Palmar muscles of man. _a_, Ligaments of wrist,
especially the anterior ligament. _c_, _c′_, Sheathing
ligaments. _d_, _e_, _f_, Oblique fibres of the ligaments
of the sheath of the flexor tendons. 1, 2, Tendons flexor
sublimis, and of the flexor profundus muscles of the fingers.
3, The reciprocal perforation of these tendons. 4, Continuation
of the tendons of the flexor profundus of the fingers. 5,
Tendon of the flexor longus pollicis. 6, Abductor pollicis. 7,
8, 9, Flexor brevis, adductor, and opponens pollicis. 10, 11,
12, Flexor brevis, abductor, and opponens minimi digiti. 13,
Lumbricales. 14, First dorsal inter-osseous muscle.
]

According to my own researches, the long abductor of the thumb in anthropoids forms a muscle not more considerable than one in proximity with it, of which the origin and more central direction recall the short extensor of the human thumb. In all four species I found that the abductor had two tendons, and was attached to the trapezium. The muscle in its vicinity is inserted above the base of the first metacarpal bone. I have not been able to discover an extra extensor of the thumb in the gorilla. The question now arises what we should think of the second muscle, which is found in these animals in the vicinity of the abductor. In my opinion, it may be confidently accepted as a short extensor of the thumb, since it always effects an extension of the metacarpal bone of that member, and in this act of extension it is supported by the long extensor which acts upon the phalanges. It must be remembered that the comparatively short thumbs of anthropoids have not to be employed in so many different ways as the human thumb, and that we cannot therefore be surprised that the development of the short extensor is less complete. A special extensor muscle of the index finger is either altogether absent in the gorilla or very slightly developed, while it is very apparent in _Hylobates albimanus_ (~6~, Fig. 53). In the chimpanzee this muscle sends a tendon to the middle finger. In the orang there is one extensor common to the four fingers. In the gibbon’s hand, this, as well as the other extensor and flexor muscles, is remarkable for its excessive slenderness. The manifold connections of the extensor tendons with each other are an interesting peculiarity (Fig. 53).

Fig. 52.--Palmar muscles of gorilla. _a_, Anterior ligament.
_b_, Remains of the skin of palm, here covered with a very
sinewy skin. _c_, _f_, Oblique fibres of the ligaments of the
sheath of the flexor tendons of fingers. 1, 2, Flexor tendons.
3, Spaces between the heads of the flexor brevis pollicis,
whence in man the tendon of the flexor longus pollicis issues
(comp. Fig. 51, ~5~). 4, 3, 3′, 5, Abductor, flexor brevis,
abductor pollicis. 6, 7, 8, Opponens, flexor brevis, abductor,
minimi digiti. 9, Dumbricales. 10, Supinator longus. 12, Flexor
sublimis digitorum. 13, Flexor minimi digiti. 14, Flexor carpi
ulnaris.
]

In the chimpanzee I observed a superficial flexor, common to the fingers, and enlarged in the region of the third and little fingers. A superficial flexor, belonging to the index finger, started from the inner condyle of the humerus, and from the back of the inter-muscular septum. The deep finger-flexor was attached to the four fingers. In the orang the first of these flexors forms a two-tendoned belly for the index finger, as well as one for the other three fingers. The deep flexor only displayed two bellies. In the gibbon, on the other hand, the superficial flexor displays four bellies.

Fig. 53.--Muscular system of the back of a gibbon’s hand. 1, The
extensor carpi radialis longior and brevior. 2, Abductor longus
pollicis. 3, Extensor primi internodii pollicis. 4, Extensor
secundi internodii pollicis. 5, Extensor communis digitorum. 6,
Extensor indicis. 7, Extensor minimi digiti. 8, Extensor carpi
ulnaris. 9, First dorsal inter-osseous muscle. 10, Continuation
of the same to index finger. 11, 12, The other inter-osseous
muscles of this region. A, The posterior annular ligament.
]

In the carpus of the chimpanzee there is, so far at least as my experience goes, a so-called sesamoid bone. It is in this instance in connection with the scaphoid and trapezium bones, just where the fibres of the anterior and posterior ligaments of the wrist pass into each other. In the chimpanzee the tendon of the long abductor muscle of the thumb sends some fibres into this sesamoid bone, while the other fibres of the tendon of this muscle, which divides into several strips, are inserted in the trapezium bone, and a few also in the base of the first metacarpal bone.

The short flexor muscle of the thumb, of which Bischoff has denied the existence, is certainly present in these animals. In the chimpanzee the lower fibres of the short abductor muscle of the thumb have their origin in the sesamoid bone. The middle fibres, of the same muscle issue from the strips of ligament attached to the sesamoid bone. On the other hand, the upper part of the muscle has its origin in the anterior annular ligament. In the orang, the lower fibres of the short abductor of the thumb likewise have their origin in the sesamoid bone, while the central fibres again start from the anterior annular ligament. The upper fibres are strong, and are inserted into the base of the first metacarpal bone. In a dissection of the orang the flexor longus pollicis sent a thin, tendinous expansion on to the bone. This sesamoid bone is also found in the gorilla, although Duvernoy and Rosenberg do not appear to be aware of its existence.[72]

In the palm of the gorilla’s hand there is a short abductor, a short bicipital flexor, an opponens, and an abductor of the thumb. The longer belly of the short flexor extending in a more radial direction, and in connection with the opponens, is only slightly developed. In the muscular system of a gorilla’s little finger we may observe an abductor, a short flexor, and an opponens. The palm of the chimpanzee displays a short abductor, an opponens, a short bicipital flexor, and an adductor of the thumb; also an abductor, a short flexor, and an opponens of the little finger. In the orang I observed a short abductor, a short flexor with two bellies, an opponens, and an adductor of the thumb. In addition to the short flexor of the thumb, Langer and Bischoff describe another short, independent muscle, representing the long flexor, and attached to the second phalanx, but I have not myself ascertained the existence of this muscle. The same anatomists mention an adductor between the third metacarpal bone and the first joint of the thumb, and another between the second metacarpal bone and the second joint of the thumb, passing on into the extensor tendon. I am myself convinced of the existence of a twofold adductor, but not of the fact that the tendon of one of the muscles (termed by Langer the second opponens) passes on into the extensor tendon. In the little finger of the orang there is an abductor, a short flexor, and an opponens. In the gibbon there is a short abductor, a faintly indicated opponens, a short bicipital flexor, and an adductor of the thumb. In _Hylobates albimanus_ this adductor divides into four or five portions, which are attached to the whole of the first metacarpal bone. In the little finger there is an abductor, a short flexor, and an opponens. In the same animal the first inter-osseous muscle is attached by one portion to the second metacarpal bone, by the other to the base of the second phalanx of the index finger (Fig. 53, ~9~, ~10~).

Bischoff has described the muscles which Halford terms _Contrahentes digitorum_ (contractors of the digits), which lie deep in the palm of the hands and feet of the chimpanzee and gibbon, the mandril, baboon, and other apes.[73] They rest upon the inter-osseous muscles, and are covered by the tendons of the long flexors of the digits, as well as by the lumbricales muscles. I have been unable to trace these _Musculi contrahentes_ in the gorilla. In a female chimpanzee I observed a _Musculus contrahens_ for the fourth, and another for the fifth finger, and the same for the fourth and fifth toes. In the orang I observed a _Musculus contrahens_ for the fourth, and one for the fifth fingers, and two faintly indicated _Contrahentes_ for the fourth and fifth toes. Similar muscles of the second, fourth, and fifth fingers, and of the fourth and fifth toes, may be observed in the white-handed gibbon.

In correspondence with the height of the pelvic bones, the gluteus maximus of these animals only displays a moderate width in comparison with its length. The tendon which attaches it to the femur extends low down, almost as far as the knee-joint. The gluteus medius and minimus are also long, in correspondence with this structure of the pelvis, although they are attached to the large trochanter, and to the posterior inter-trochanteric line. The climbing muscle (_Musculus scansorius_), which extends between the hip-bone and the condyles of the femur, was discovered by Troill in the chimpanzee, and by Bischoff in the orang, and is described by them as strongly made; it appears to be absent in the gorilla and the gibbon. The pyriformis generally forms portions of the neighbouring muscles. The tensor vaginæ femoris, which is strong and wide in most anthropoids, is either greatly reduced or altogether absent in the orang. The sartorius is not, as in man, attached to the inner surface of the tibia, just below the internal tuberosity, but it is inserted much lower down on this surface. In the gorilla it has a tricipital attachment, one to the deep fascia of the thigh, and two others to the internal border of the tibia. In the chimpanzee and the gibbon the muscle extends equally low down. In the orang it does not go so far, but the _gracilis_ and _semi-tendinosus_ are in the same relative position. The biceps of the femur is very apparent in the orang; its long head divides in two parts, of which the lower is inserted in the fibula, and is here united with the short head.

Bischoff at first denied the existence of the plantaris in the chimpanzee, and Brühl had previously done the same, but it is as normally present in that animal as in man, in whom also it is sometimes absent. I, however, as well as other observers, have failed to discover it in the gorilla, orang, and gibbon. The popliteus is developed in every instance. The tibio-fibular muscle (_Musculus peroneotibialis_), covered by the popliteus, of which the existence was ascertained by Gruber, has not been observed by me in any of the anthropoids, with the exception of the chimpanzee. But it was very apparent in a red sea-cat monkey (_Cercopithecus ruber_).