THE ANATOMY OF APES
To describe generally the anatomy of apes would be, in fact, to describe in an elementary manner the general anatomy of man. It is necessary, therefore, here to assume that the reader has already an elementary knowledge of human anatomy, and to refer such readers as have not such knowledge to the article ANATOMY.
THE EXTERNAL FORM AND CLOTHING
The difference in bulk between the different members of the group (e.g. Troglodytes and Hapale) is extreme, being greater than that between a man and a common squirrel.
The proportions of the body as regards the relative lengths of the two pairs of limbs one with the other, and both with that of the trunk, vary considerably. Both pairs may be much elongated, as in Ateles and Hylobates, and either sub-equally, as in the first of these genera, or with the arms very greatly in excess, as in the second. The legs may be excessively short, and the arms, at the same time, excessively long, as in the orang. Both pairs may be short and sub-equal, as often in the Cynopithecinoe. Only in the Nyctipithecinoe and Hapalinoe does the excess in length of the lower limbs over the upper exceed or equal that which is found in man. The length of the tail presents some noteworthy points. At its first appearance it is found at once at its greatest absolute length, and also greatly developed relatively, being about twice the length of the trunk. Its greatest relative length is, however, attained in Ateles, where it reaches three times the length of the trunk. The constancy of the degree of its development varies much in different groups. In the greater number of genera it is long all the species, and in some (Simia, troglodytes, and Hylobates) it is absent in all. In others it may be long or short, or completely absent, e.g. in Macacus.
The form of the head presents great differences-it may be rounded, as e.g., in Ateles; produced vertically, as in Simia; drawn out posteriorly to an extreme degree, as in Chrysothrix; or anteriorly, as in Cynocephalus. A production of the muzzle, necessitated by the presence of large teeth, exists already in troglodytes; but in the baboons, not only is this prolongation carried much further, but the terminal position of the nostrils gives an emphatically dog like aspect to the face.
The eyes may be small compared with the size of the head, as in the baboons, they may, on the contrary, attain a relatively enormous size, as in Nyctipithecus. They are always forwardly directed, and never much more separated one from another than in man. They may, however, be much more closely approximated, as notably in Chrysothrix.
The external ears are always well developed, and have very generally their postero-superior angle pointed. They may be large and small in the same genus, as in Troglodytes. Only in the gorilla do we find present, even in a rudimentary condition, that soft depending portion of the human ear with is termed the "lobule."
The nose has scarcely ever more than a very slight prominence, and yet an enormous development is to be met with in Semnopithecus nasalis; while in S. roxellance we find a sharply prominent, though smaller and extremely upturned, nose. The hoolock gibbon also possesses a prominent but slightly aquiline nose, the terminal position of the nostrils in Cynocephalus has been just mentioned. These apertures may be closely approximately, as in all the Simiadoe, or they may be separated one from the other by abroad septum, as in the Cebidoe, its breadth, however, varying somewhat in different genera, as, e.g. in Ateles and Eriodes, and in Callithrix and Byctipithecus.
The lips are generally thin, but may be very extensive, as in Simia.
The hands are generally provided with thumbs, though these organs (as in Colobus and Ateles) may be represented only by small nailless tubercles. The thumb (pollex) is more human in its proportions in the chimpanzee than in any other of the highest apes. As compared with the length of the hand, it is most man-like in the lowest Cabidoe, e.g., Chrysothrix and Hapale. In spite of greater relative, length, however, it may but little merit the name of thumb, as it is but slightly opposable to the other digits in any of the Cebidoe, and is not at all so in the Hapalinoe.
The hallux (great toe) is never rudimentary like the pollex. It is never, as it often is in man, the longest digit of the foot, but is constantly the shortest one. As compared with the entire length of the foot, it is most human in the chimpanzee and some gibbons, and smallest of all in the orang, and next smallest in Hapale. More detailed proportions will be more appropriately given in speaking of the skeleton.
Every digit is provided with a nail, except the hallux of the orang and those rudimentary tubercles already spoken of as representing thumbs in Ateles and colobus. The nail of the hallux is flat in every species, but the other nails are never so flat as are the nails of man. The lateral compression of the nails becomes more strongly marked in some Cebidoe, e.g., in Eriodes, but attains its extreme in the Hapalinoe, where every nail, except that of the hallux, assumes the form of a long, curved, and sharply-pointed claw.
All the apes, without exception, differ from man in having the body almost entirely clothed with copious hair, and especially in never having the back naked. In the gibbons, the semnopithecinoe, and the Cynopithecinoe, naked spaces (ischiatic callosities) are present on that part of the body which is the main support in the sitting posture. These naked spaces increase in size as we descend through the series of Cynopitheinoe, and are subject to a tunefaction (sometimes excessive and extending to parts adjacent) at the season of sexual excitement. Such naked spaces are never found in any of the Cebidoe. No ape has so exclusive and preponderating a development of hair on the head and face as exists in most men. As to the head, long hair is found thereon in Hapale Oedipus and in some of the Semnopitheci, whilst certain of the Macaci (as, e.g., the Chinese bonnest moneky, M. sinicus) have the hair of the head long, and radiating in all directions from a central point on the sinciput. A beard is developed in the male orang, and Cercopithecus Diana has long hair on the cheeks and chin. The wanderoo (Macacus silenus) has the face encircled by a kind of mane of very long hairs, and many of the marmosets have a long tuft of hairs on each side of the head. The American apes exhibit some extremes respecting hair development. Thus in some of the howlers (as in some of the Colobi of the Old World) the hair of the flanks is greatly elongated. Some also have an elongated beard, but the latter structure attains its maximum of development in the couxio (Pithecia satanas). Some of Pitheciinoe have the hair of the whole body and tail very long, others have the head of the female furnished with elongated hair, while another species (Brachyurus calvus) has the head bald. Long hair may be developed from the shoulders, as in Cynocephalus hamadryas and Hapale humeralifer; or many form a tuft at the end of the tail, as in Macacus silenus, Cynocephalus hamadryas, and Cynocephalus gelada.
The direction of the hair may sometimes vary in nearly allied forms. Thus the hairs on the arm and forearm respectively may be so directed that the apices converge towards the elbow. Such is the case in most of the latisternal apes, yet in Hylobates agilis all the hair of both these limbs segments is directed towards the wrist.
The hair presents generally no remarkable character as to its structure. It may, however, assume a very silky nature, as in Hapale rosalia, or assume the character of wool, as in Eriodes, and as in that remarkable form recently discovered by Father David, Macacus thibetanus. The last named species inhabits the snowy ranges of the Thibet mountains, and is provided for this habitat by a modification in its hairy clothing similar to that which suited the extinct mammoth for the severity of its Siberian home. This fact as to M. thibetanus has an interesting bearing on fossil forms, which we shall have to consider later.
Great brilliance of colour is sometimes found in the naked parts of the body, particularly in the Simiadoe, and especially in the regions of the face and sexual organs. In some of Cercopitheci and Cynocephali, rose colour, turquoise blue, green, golden yellow, and vermilion appear, in various combinations, in one or other or both of these regions, and become especially brilliant at the epochs of sexual excitement.
THE SKELETON
The skeleton of apes generally, if we except the tail, consists of but few more bones than that of man. The proportions of its parts, except as regards the relative length of the limb bones, are also much as in man; nor are their shapes, except those of the jaws and haunch bones, greatly different. The same general resemblance may be predicated of their minute structure, though the osseous tissue is generally rather dense, and the medullary cavity in the long bones small.
The Axial Skeleton. -- The Skull
The axial skeleton consists of the skull and the vertebral column, and the general shape of its more anterior portion, the skull, has already been indicated when speaking of the head as part of the external form. It is scarcely ever so evenly balanced on the occipital condyles as in man.
The artificial division of the skull into a cranial and a facial portion may be here conveniently adopted from human anatomy. The proportion of the latter portion to the former varies greatly from age and sex, owing mainly to the differences produced through the development of large and powerful canine teeth in the adult males of most species. This proportion also varies in an irregular manner as we descend (through the series of apes) from those which are most like man. Thus the facial part is already very large in the orang and chimpanzee, much more so than in Semnopithecus, where most of the ape cranial characters are moderately developed, or even than in many Cercopitheci; but it attains its maximum of relative size in the Cynocephali, above all in C. porcarius. In the Cebidoe the facial part is relatively smaller than in the Simiadoe, with the exception of Mycetes, while in Chrysothrix the facial portion of the skull is relatively smaller than even in man himself. The relation of the face to the cranium (or brain case) is best shown by the craniofacial angle, which is estimated by means of two lines, one drawn parallel to the base of the skull (from the front margin of the occipital foramen to the anterior end of the cerebral surface of the presphenoid), the other drawn from the front end of that base to the middle of the lower margin of the upper jaw.
No ape, especially no ape of the Old World, presents to elevated and rounded a contour in the frontal region as does man. It is in American forms, especially in the genus Pithecia, that we find the greatest resemblance to man in this respect; but the skiull is lofty in the orang.
The convexity of the occiput is well marked in Simia, Troglodytes niger, and Hylobates, while in the inferior Simiadoe it is flat. Its maximum of production, however, is met with in the genus Chrysothrix.
Ridges for muscular attachment, or other bony prominences, more or less disguising the rotundity of the cranium, are very generally developed, except in the smallest species. Such ridges are met with at once at their very maximum of extent in Troglodytes gorilla. In that animal an enormous sagittal ridge traverses the middle of the sinciput antero-posteriorly, joinging at its hinder end a prodigious lambdoidal crest for the insertion of the muscles of the neck. A very largely developed supra-orbital ridge runs transversely above the orbits, which it obliquely overhangs. The orang has no supra-orbital ridge, but in the other large Simiadoe all these ridges are more or less developed, and moderate sagittal and lambdoidal ridges are found in Mycetes, Cebus, Pithecia, and some other of the Cebidoe.
The mastoid process never attains in apes the large relative size it has in man; but it is prominent in the baboons and larger Macaci, as well as Troglodytes, its development bearing relation to the size and weight of the head. As the mastoid diminished we find that the under surface of the petrous bone assumes a swollen or "bullate" condition.
The orbits are in T. gorilla much as in man, but in the orang they are more rounded. They become very large ins Hylobates, but attain an enormous size in Nyctipithecus. The extent to which each orbit opens into the adjacent temporal fossa, i.e., the size and shape of the sphenomaxillary fissure, varies considerably. It is narrow and much elongated in the gorilla and in Cynocephalus; it is short in the Semnopithecinoe and in Ateles, but opens widely so as to expose the vidian foramen. It is most completely closed of all in Mycetes, where it sometimes all but disappears entirely. The olfactory chamber is narrow and deep in the lower Simiadoe. The cribriform plate of the ethmoid is generally separated from the presphenoid by the junction of the orbital plates of the frontal. Such, however, is not the case in the orang and chimpanzee, though it is so in the gorilla and in Hylobates.
The plane of the foramen magnum, as compared with the basi-cranial axis, varies with the projection of the occiput. It generally forms a less open angle with that axis than in man, but in Chrysothrix the angle is yet more open than in the human skull.
The zygomata are arched both outward and upwards in the gorilla and some baboons, but decrease in relative as well as absolute size the smaller forms,-notably in Chrysothrix. No long slender styloid process is normally attached to the skull, though such may be able case in Cynocephalus. The vahinal process never attains the size it does in man, though it is considerable in the gorilla, and sometimes noticeable in Simia. A bony meatus auditorius externus exists in all the Simiadoe, and is absent in the whole of the Cebidoe. In Nyctipithecus the ali-sphenoid is almost shut out from the parietal by the close approximation of the squamosal to the malar. In Cebus there is often a large malar foramen.
The premaxillary bones have throughout the apes a distinctness of development and a relative size not found in man, the sutures separating them from the maxillaries remaining visible, with the exception of the chimpanzee, after the adult dentition has been attained. The maxillaries themselves develop great swollen tuberosities in the Cynocephali, and a similar structure is developed even in Macacus niger.
The nasal bones are small, generally flatter than in man. In the orang they are quite flat. They are convex in some of the Semnopitheci and in the Cynocephali, but the proboscis monkey has its nasal bones no more developed than have other species of its genus. The nasals seem to attain their maximum of relative size in Mycetes.
The lower jaw, or mandible, is always in one piece in adults. It is most man-like in the siamang, since we there alone find a slight chin. On the other hand, in Hylobates the angle is produced downwards and backwards, and we find the same in Hapale. Its maximum of relative size is attained in Mycetes, where the very broad ascending ramus serves to protect and shelter the enormously developed body of the hyoid.
Air cells may be developed, as in the gorilla, in the parts adjacent to the mastoid. Frontal sinuses are generally absent in the Simiadoe, being replaced by a coarse diploe. We find them, however, in the Cebidoe, and in Cebus they are often larger than they are in man. The total length of the cerebral cavity is never so much as 2 x times the length of the basi-cranial axis.
The sutures of the skull become entirely obliterated with age. In the gorilla the sutures assume as more dentated structure than is found in any other ape or in man. The internasal suture becomes early obliterated in most of the Simiadoe. The tentorium is sometimes ossified, as in the Cebinoe and Mycetes. From Hylobates downwards there is a small cerebellar fossa on the I nner surface of the petrosal.
The Vertebral Column
The vertebral or spinal column in all apes consists of the same regions as it does in man, and, with the exception of the coccygeal or caudal portion, these regions bear more or less the same proportions one to another as they do in him. That beautiful sigmoid curvature which exists in the human spine is not found in any ape; but the nearest approximation to it is found, not in the Simiinoe, but in the cynocephali. In the latisternal apes the spinous processes are directed as in man, but in the rest their apices converge towards a single point in the back.
The cervicalregion is relatively more elongated than in man in Hylobates, Cynocephalus, and Ateles. The atlas is very man-like in Troglodyres and Simia, except that its transverse process is rather smaller and shorter relatively, and more curved dorsally. Except in Ateles and the Simiinoe, it is almost always perforated by the vertebral artery, instead of being merely grooved by it. In cynocephalus the atlas is exceedingly massive, and may, by very rare exception, develop a spinous process. The spines of the cervical vertebrae do not bifurcate beyond the second, and generally the spine of the seventh vertebra is the longest, at least with the exception of that of the axis. In the gorilla, and orang, however, the spines of the third, fourth, fifth, and sixth vertebrae are exceedingly elongated and longer than that of the seventh. The cervical neural laminae are wider antero-posteriorly, the vertebral column being supposed horizontal, in Hylobates and Ateles than in other forms. Beneath the anterior articular process (prezygopophysis) a marked prominence -- the metapophysis -- may be developed, and is particularly conspicuous in Ateles. The costal plate of the esixth cervical is almost always larger than the homologous part in the other cervicals; but it predominates least in the chimpanzee and Nyctipithecus. The length of each centrum, compared with its breadth, is already greater in Troglodytes and Simia than in man. In others the dimensions are about equal, except that in Cynocephalus, Ateles, and Mycetes the length slightly exceeds the breadth.
The dorsal vertebrae vary in number from eleven, as sometimes in Cercopithecus and Macacus, to fourteen, as sometimes in Hybobates, or even to fifteen, as in Nyctipithecus. In the Cebidoe, above the Hapalinoe, the number rarely falls below thirteen. In the orang the number is, as in man, twelve; in troglodytes it is thirteen. The proportion of this region does not increase regularly with the number of its vertebreae. It attains it greatest relative length in Ateles, where it is over nine-twentieths of the total length of the spine without the tail; while in Nyctipithecus it is relatively shorter than in troglodytes or Simia. The increase in transverse diameter of the bodies of the vertebrae, as we proceed from before backwards, is exceptionally great in Hylobates and Cynocephalus. The lumbar region contains from four to seven vertebrae. In the Simiinoe and Cebinoe there are four or five, though in Cebus the number is often six. Its relative length is greatest in Nyctipithecus, Chrycothrix, the Semnopithecinoe, and Cynocephalus. It is least in the Simiinoe, and Ateles. The number of dorsal and lumbar vertebrae, taken together, is seventeenth in troglodytes and Simia, eighteen (mostly) in Ateles and Hylobates, and nineteen in the rest. In most forms the dorsal and lumbar regions are about equal in length, but the lumbar region is the shorter in the Simiinoe, and less than half the length of the dorsal in the gorilla. The lumbar, spinous processes are vertical, or project backwards in the Simiinoe and in Ateles; in the other forms they project strongly forwards, especially in the lower Cebidoe. The lumbar transverse processes always project outwards, more or less at right angle to the axis of the spine, or else forwards. In the Simiinoe and Ateles they are never inclined ventrally, but in some of the lower Simiadoe they begin to be so; in the lower Cebicoe they are so very decidedly. Only in Troglodytes and Simia are they inclined somewhat dorsally. In the last two general the lumbar vertebrae are broader than their length; in most other forms length is in excess. The length of the individual lumbar vertebrae, compared with the dorsal (e.g., the longest lumbar with the ninth dorsal), is greatest in the lower Cebidoe, rather less in the lower Simiadoe, and least in the Simiinoe.
The sacrum attains its greatest abslute length in the gorilla, but is relatively longer than in man in all the Simiinoe. Of all the inferior apes, Hylobates has the relatively longest sacrum. The number of vertebrae included in the sacrum varies more or less with age. In the apes below the Simiinoe there are generally only two or three sacral vertebrae. In Ateles, Hylobates, and Brachyurus, there may be four; while in the Simiinoe there are always five, and sometimes six sacral vertebrae. In most apes the sacrum and lumbar vertebrae appear to lie in one slightly curved line. Troglodytes presents in this respect a great contrast to the human structure. In Simia the sacro-vertberal angle is rather more marked; but sometimes in Cynocephalus it is so much so as almost to rival that of man. The same may be said of the concavity of the anterior surface of the sacrum. It is most marked in the Cynocephali, and is more so in Simia than in troglodytes. The sacrum gradually tapers posteriorly in Troglodytes and Simia, and more or less so in Gylobates. In the other Simiadoe, however, the sacrum is very wide at its anterior end, and it then very rapidly contracts backwards, so that the transverse diameter of the third sacral vertebra is very much narrower than that of the first. In the Cebidoe generally, and especially in Ateles, the contraction is not so marked.
The caudal vertebrae are always more than four in number, except in the Simiinoe and in Macacus inuus. In Cynocephalus mormon (the mandrill), however, there are sometimes only five vertebrae. The short-tailed Macaci and Brachyuri have from about fifteen to seventeent caudal vertebrae, the shortness of the tail being occasioned rather by a diminution in the size of the component vertebrae than by a decrease in their number. In the other forms the number varies between twenty and thirty-three, the latter being the number attained in the genus Ateles. The proportion borne by this region of the spine to all the more anterior parts is greatest in Ateles, almost three to one; in the other longest-tailed genera it is rarely so large as two to one. The absolute length of the tail is greatest in the Semnopithecinoe, where also the individual caudal vertebrae attain their greatest length, namely, two inches. The caudal vertebrae generally increase in length as we proceed backwards from the sacrum, till about the seventh, eight, or ninth, which, with the tenth and eleventh, are the longest caudal vertebrae in most long-ailed forms. In Ateles, however, it is the eleventh, twelfth, thirteenth, and fourteen vertebrae that are the longest. In the Simiinoe and in Inuus the caudal vertebrae decrease in length as we proceed backwards. Except in the forms just named, all the first four caudal vertebrae possess a complete neutral arch, sometimes six are so provided, but only in Ateles does the number attain eight. With the same exceptions, again, the first four caudal vertebrae unite by articular processes, while transverse processes (single or antero-posteriorly double) exist in a great part of the tail. In Ateles the caudal vertebrae are (as might be expected from the very prehensile character of the tail) exceptionally provided with bony processes serving as points of muscular attachment. Chevron bones and processes for their attachment are altogether wanting only in the Simiinoe and in Macacus inuus. They attain their maximum in Ateles, where they present almost every variety of development in one or other part of the caudal region.
Certain vertebral processes, which in man are generally inconspicuous, and which are but little developed in the Simiinoe, attain in lower forms a marked development. These are the metaphophyses and anapophyses. The first of these generally appear about the eight or ninth dorsal vertebrae, and may thence be traced backwards into the anterior caudal vertebrae, where they end by coalescing with the prezygopophyses. In Ateles these processes may sometimes be traced as far forward as the third cervival vertebra. The anapophyses become, below the Simiinoe, very conspicuous, projecting outwards and backwards from one vertebra, and embracing the prezygophyphysis of thevertebra next behind. Generally they may be traced from the eight or ninth dorsal vertebra to the penultimate lumbar vertebra. They attain their maximum of relative size in the lower Cebidoe. They may (as sometimes in Ateles abd Cynocephalus) be traced on to the posterior cervical vertebrae, while they appear to coalesce with the transverse processes in the tail, and thus they may be developed almost throughout the vertebral column. The Cebidoe often develop hyperapophyses in the last dorsal and in the lumbar vertebrae. These processes are some what similar to anapophyses, but are placed much higher, and each pair embraces the spinous process of the vertbera next behind.
In most apes the sternum is quite narrow, and consists of a more or less enlarged manubrium, followed by a chain of sub-equal and antero-posteriorly elongated bones from three to six in number. In the Simiinoe alone do we find a broad sternum, or one consisting of a manubrium, followed by one bone only, as in Hylocates. The orang present a singular peculiarity, in that the breast-bone long remains made up of oassifications arranged in pairs, side by side, successively. The total number of ribs has already been indicated in speaking of the dorsal vertebrae. The true ribs are seven in number on each side in the highest forms, but in Hylobytes there are sometimes eight. In Ateles there are sometimes nine pairs. In Hapale the number varies from six to eight, and it is seven or eight in the other genera. The "angles" of the ribs are never so marked as in man. They are most marked in Hylobates. Pitchecia is distinguished by the greater relative breadth of the ribs. In no ape is the thorax half as broad again as it is deep from back to breast. Nevertheless, in the Simiinoe, its transverse diameter exceeds its doeth by both about one-fourth to a little under one-third of the latter. In Ateles (and sometimes also in Mycetes) the thorax is wider than it is deep, but in all the rest it is narrow, being deeper than it is wide.
The Appendicular Skeleton
The development of this part of the skeleton has been indicated in a general manner in speaking of the external form. The length of the pelvic limb compared with the pectoral one-the foot and hand being removed-attains in no ape the proportion that it does in man, i.e., 145 to 100; the neatest approximation being made by Nyctipithecus and Callithirx, namely, about 137 to 100. the length of the foot, compared with that of the hand, is exceptionally small in the Simiinoe, namely, from 84 up to 115 to 1000. its greatest relative length is in Chrysothrix, viz.,about 177 to 100. in man it is about 134 to 100. the entire pectoral limb (measured from the summit of the head of the humerus to the distal end of the longest digit) is absolutely longest in the gorilla and orang. Its proportion to the spine is greatest in Hylobates, where it may attain the proportion of 222 to 100. next come Ateles 174, Simia 170, the gorilla 150, and the chimpanzee 152. the rest vary from 121 to a little shorter than the spine, except certain of the lower Cebidoe, thus in Chrysothrix and Hapale it is less then 84to 100. only in the simiione and in Ateles is the pectoral limb, without the hand, shorter than the spine.
The scapula of the gorilla present a remarkable likeness to that of man, but that of its congener, the chaimpanzee (the posterior vertebral angle being so acute), is less like man's than is that of the oang. The size of the supraspinous fossa, as compared with the infra-spinous one, attains, its maximum in the gorilla and Mycetes. In Simia and the Pitcheciinoe the supra-spinous fossa is exceptionally small. The margin, corresponding with the superior margin of man's scapula, is generally convex in the forms below the Simiione (except Ateles and Pitchecia), and attains its maximum of convexity in aged Cynocephali. A suprascapular notch is not well defined in the great majority of the Simiadoe, but in some of the Cebudoe (Ateles and Mycetes) it is constantly, and in other often, so enclosed as to become a foramen. In Mycetes a remarkable flat process springs from the bridge of bone encircling this foramen. This process exists in no other genus. The surface for the teres major musvcle projects out very strongly in the Cynopithecinoe and in Cebus and Chrysothrix. The acromion and coracoid processes are short in the lower Simiadoe; both are long in the Simiinoe and in Ateles.
The clavicle is well developed in every species of the order, and that of the orang is absolutely the largest; and it is longest, compared with the spine, in that animal and in Hylobates, being as 28 or 32 to 100, while in the lower Vebidoe it may be less than 12 to 100. This bone is exceptionally slender in Mycetes, and is broadest in Troglodytes and the Cynopithecinoe. In the lower Simiadoe a fossa is excavated beneath the arcomial end of the bone. Rarely, as in Simia, there is a very prominent deltoidal ridge.
The humerus presents in all apes the same fossae and prominences as in man. Its length, as compared with the spine, is in Hylobates 70 or 80 to 100; but in most apes its length, thus compared, is between 45 and 30 to 100. The articular surface of the head is directed backwards and inwards, instead of almost exclusively inwards, as in man. In this respect man is most resembled by the Simiinoe. The tuberosities may project upwards slightly above the articular head, as in Cynocephalus. General they are about on a level with its top, but may be decidedly below it, as in Ateles, Hylobates, and Simia. The radial border of the bicipital groove may be very prominent, as in Cynocphalus. The groove may be spanned by a bridge of bone, as sometimes in the chimpanzee. The position of the nutrients foramen varies even in different individuals. The supinator ridge is especially developed in Cynocephalus, Cebus, and Hapale. In the Simiinoe it is only slightly developed. The external condyle is distinct in the Simiinoe; in the other genera it is closely applied to the capitellum. A surpra-condyloid foramen is never present normally in the Simiadoe, but is present or less constantly in the Cebidoe, from Cebus downwards, being perhaps most frequently absent in Hapale. Through this canal the brachial artery and median nerve pass. The projection of the radial margin of the trochlea is most prominent in the Simiinoe and Hapale. It almost disappears in the Cynopithecinoe. The radius and ulna are never amkylosed together in apes. They diverge most, medianly, one from another in the gorilla. The radius is four-fifths the length of the spine in Hylobates, and three-fifths in Simia and Ateles. Mostly it is between three-tenths and two-fifths of the length of the spine, but may, as in Hapale, be only a quarter. The total length of the radius rather more frequently falls short of, than exceeds, that of the humerus. It exceeds it in Simia, Hylobates, Ateles, Cynocephalus, and sometimes in the Semnopithecinoe. In all the others it falls short- in none, however, so much so as in man, Brachyurus approximating most to the human proportion. The radius is stoutes in Cynocephalus, slenderest in Ateles, and, above all, in Hylobates. The ulna varies, like the radius, in length and breadth. The olecranon is broad in the Simiinoe, but in the lower apes it is relatively larger, especially in Cynocephalus and Mycetes. The styloid process is very long in Hylobates, where it developed a prominence, on its hinder side, for the internal lateral ligament of the wrist. In Ateles this process is extremely long, having, as it were, a rounded articular head placed at the end of peduncle. The ulna articulates with the carpus in all the apes except troglodytes and Simia.
The skeleton of the hand attains its greatest bulk in the gorilla, but its greatest length in the orang. It may be more than half the length of the spine in Hylobates, and hardly less in Simia and Ateles. It may be but a fifth, as in Chrysothrix.
The carpus consists, in Troglodytes, of the same eight bones as in man. In all the other genera there is a ninth bone, the intermedium. Only in Hylobates does the length of the carpus considerably exceed its breadth-as 100 to 82. The nearest approach to this is made by Ateles, where the length is to the breadth as 100 to 107. The scaphoides may, as in the gorilla and lower Simiadoe, develop a large tuberosity. The intermedium has a flattened proximal surface, which joins the ulnar part of the concave distal articular surface of the scaphoides. Its distal surface is in general deeply concave antero-posteriorly, and embraces the radial side of the head of the magnum. The bone appears to answer to part of the scaphoid of man. The cuneiforme, except in Troglodytes and Simia, articulates directly with the ulna. The pisiforme is small (as in man) in Simia and Ate;es; it is very large in the gorilla and Cynocephalus, and long but slender in Hylobates. Commonly it contributes to form, with the cuneiforme, a cup for the cereption of the end of the styloid process of the ulna. The trapezium has sometimes, as e.g., in the gorilla and Hylobates, a very large radial tuberosity. The surface for the reception of the first metacarpal is convex from the dorsal to the palmar surface of the bone, and sometimes it is more or less concave in the reverse direction, but this concavity is never so strongly marked as in man. In the highest apes there appears to be much irregularity as to its development. In Hylobates there is no trace of any concavity, but a strongly convex and rounded tubercle receives the articular cup of the base of the first metacarpal. In the lower Simiadoe the concavity is sometimes present, and sometimes in the Cebidoe (as, e.g. occasionally in Cebus and Brachyurus) a small saddle-shaped surface may be found. In Ateles the trapezium is large in spite of the rudimentary condition of the pollex, but there is no saddle. The trapezium is always so placed that the axis of the convexity of the saddle forms a marked angle with a line drawn across the articulations of the four outer metacarpal bones with the proximal row of carpals. In the gorilla this angle is, as in man, very open; but in the chimpanzee and lower Simiadoe it is smaller, the trapezium being, as it were, somewhat more pressed inwards, at its radial end, towards the middle of the palm. In the American apes the trapezium is well set out; and this, no doubt, contributes to produce that very feeble opposition and palmad flexion of the pollex which have been noticed as existing in them. The magnum is not generally the largest carpal bone, but rather the unciforme, which latter has its palmar process sometimes very much produced, as is the case in Hylobates. The metacarpus attains its greatest absolute length in the third metacarpal of Simia. This segment may, as in Hylobates, attain the proportion of one-fifth the length of the spine. The metacarpals are longer and narrower proportionally in apes than in man.
The phalanges are the same in number in apes as they are in man, except that in Ateles and Colobus the pollex may have but one small nodular phalanx or none. the phalanges are generally more curved than in man, and, except in the Hapalinoe, the ultimate phalanges are always flattened from dorsum to palm. In the Hapalinoe they are laterally compressed, curved, and pointed to support the peculiar claws of that sub-family. The length of the pollex with its metacarpal bears a much greater proportion to that of the spine un Hylobates and Simia than in man. With the exception of Ateles and Colobus, the shortest thumb, thus estimated, is found in Nyctipithecus and Chrysothrix, namely,11 to 100.
The pollex without its metacarpal, compared in length with the manus, is shortest (voz., as 17 to 100) in Hylobates, and longest (viz., as 32 to 100) in Hapale. The pollex, when brought beside the index digit, rarely extends so far as in man, and does so only in the Cebidoe, where, in the Hapalinoe, it may reach nearly to the distal end of the proximal phalanx of the index. In cynocephalus it may reach the middle of that phalanx, while in Troglodytes it reaches but very little beyond its proximal end.
The entire pelvic limb, meadsured from the summit of the femur to the distal end of the longest digit, is absolutely greatest in the gorilla, and then in the orang and the chimpanzee. If the pes be removed, then the leg of the chimpanzee is longer than that of the orang.
Compared with the length of the spine, the entire pelvic limbs of Hylobates and Ateles are longest, namely, as 162 or 169 to 100. That of Hapale is the shortest, being but as 110 to 100. Without the pes, the leg of Hapale is also shortest relatively compared with the spine, namely, as 77 to 100; while that of Hylobates is longest, namely, as 125 to 100. the os innominatum is in every species strikingly different in form from that of man. In absolute size this bone attains its maximum in the gorilla, where it is much larger than in man, and where the ilium is very broad. The external surface of the ilium is generally more or less concave, and concave only. In Troglodytes and Simia, however, it is more or less convex, but not as in man, and therefore there is no sigmoid curvature of the crest of the ilium, and there are no distinct gluteal lines. The internal surface of the ilium is generally narrow and flat, or only slightly concave, except in the gorilla. The tuberosity of the ischium is always a marked and more or less rugose enlargement of the bone; but in the Simiadoe below Troglodytes it is flattened and very much developed, and so much everted that sometimes (in Cynocephalus) its transverse exceeds its antero-posterior diameter. In the Cebidoe it again becomes small, and more or less rounded.
The spine of the ischium is generally very small, yet distinct. Only in Simia does it attain a considerable sharpness and prominence. The great sciatic notch is never very deep and concave, as in man. It is most concave in the gorilla, the orang, and in Cynocephalus. The lesser sciatic notch is generally represented by a margin which is so slightly concave as to be almost or quite straight save through the eversion of the tuberosity. The projection of the spine of the ischium produces in man a deep notch such as exists in no ape. The cotyloid notch, and the excavation continuous with it, are constantly present, even in Simia, where, however, it is very small and narrow, in harmony with the absence of the ligamentum teres.
The femur's length, compared with that of the spine, is as 67 to 100 in Hylobates, 61 in Ateles, 54 in the gorilla 47 in Simia. It is shortest in Chrysothrix, 40, and Hapale, 37. In the Simiinoe it is shorter than in the humerus, its proportion to which in Simia is as 73 to 100. only in some of the Semnopithecineo does its length exceed that of the humerus more than it does in man. The shaft of the femur is sometimes nearly straight, as in Hylobates and in most Cebidoe. The femur is stoutest, relatively as well as absolutely, in the gorilla. It is slendered in Hylobates. The neck of thefemur is longest in Simia and Hylobates; shortest in Hapale. Except in the Simiinoe and in Mycetes, the great trochanter is pointed at its upper end. The trochanteric fossa is shallow in the gorilla, but is in most forms deep. The lesser trochanter is at its minimum of relative size in the Simiinoe, and is largest relatively in Hapale, and the posterior surface of the femur is in that genus wide and flat between the trochanters. The pit for the insertion of the ligamentum teres is always present, except in the orang and gorilla, where it is absent almost constantly in the first ape, occasionally in the second. In the Simiinoe, Ateles, and Lagothrix the internal condyle projects considerably further backwards than does the external one. The angle formed by the neck of the femur with the shaft varies from about 155o (Simia) to 128o (the gorilla)
The tibia and fibula never become ankylosed together. The tibia is absolutely longest in the gorilla. Its length, compared with that of the spine, is never so great as in man, except in Hylobates, in which it is slightly longer relatively. It is shortest in Mycetes, about as 37 to 100. its length is generally less than that of the femur, but sometimes, in Hapale, it slightly exceeds it. It is never, however, so short compared with the femur as in man. The crest of the tibia is not so sharp as in man. The shaft is sometimes straight, as in Lagothrix and Pithecia, sometimes considerably curved, as in the gorilla and lower cebidoe. The nalleolus is generally well-developed, but sometimes, as in the orang, very short. Its articular surface is sometimes nearly at right angles with the inferior surface of the shaft of the tibia, as in the chimpanzee; sometimes it forms an obtuse angle with that surface, as in the gorilla, and still more in the orang. The distal articular surface of the shaft of the tibia is rarely horizontal, as in Ateles and Lagotrix. In the Simiadoe and lower Cebidoe the outer portion rises so that the articular surfacr slopes upwards peronead. The fibula has its malleolus much produced outwards, projecting only about as much as, or rather than, the tibial malleolus, where as in man the fibular malleolus is much deeper than the tibial one.
The length of the pes (or foot) is absolutely greatest in the orang and gorilla. Estimating the spine as 100, the length of the pes is as much 52 in the orang; it approximates to man (35 to 100) most in the lowest Simiadoe, and in Chrysothrix- 36 to 100. The proportional length of the pes to be rest of the pelvic limb is greatest hin Simia (58 to 100), then in Nyctipithecus and Hapale (50 to 100), but never falling quite so low as in man, where it is 30 to 100. Its length, as compared with that of the tibia, is greatest in Simia (122 to 100). In all the rest it is more than four-fifths, except sometimes in Hylobates, which however is never so small as in man, i.e., as 67 to 100. the length of the pes, compared with that of the manus, is greatest in Chrysothrix (177 to 199). In Ateles it sinks to 113 to 100, and in Hylobates to 85 or 84 to 100.
The absolute length of the tarsus is never so great as in man, though that of the gorilla is nearly as long. The rest of the foot is so much longer relatively in apes than in man, that, whereas in him the proportion of the tarsus to the whole pes is as about 46 to 100, it is only 39 to 100 in the gorilla, which in this respect approaches nearest to man. The proportion sinks to 26 to 100 is Simia and Ateles, and 27 or 28 to 100 in Hylobates. Only in Simia and Hylobates is the tarsus ever less, or only a very little more, than twice the length of the carpus. The tarsus consists, constantly of the same seven bones as in man, and these bones are so arranged, or bound together by ligaments, as to form a transverse and an antero-posterior arch. In no ape, however, do the distal ends of the inner metatarsals form the anterior point of support of the anteroposterior arch, as in man. The os clacis is always, except in the gorilla, shorter compared with the spine than in man. The tuberosity may be produced upwards or downwards, or both, and is concave or grooved behind, except in the gorilla. In no ape are the long axis of the heel or the peroneal and tibial surfaces of the os calcis so vertical as they are in man; but the bone is always more or less twisted, so that the sustentaculum tali forms a more or less acute angle with the long axis of the tuberosity instead of a right angle, as in man. The twisting of the os calcis is very slight in Simia and Pithecia, and not great in Ateles and Hylobates. It is more marked in the lower Simiadoe, and more so still in Troglodytes. A narrowing of that part, which answers to the plantar surface of man, accompanies this in-twisting. In the gorilla that part of the os calcis which is behind the articular surface for the astragalus exceeds in length all the bone anterior to the hinder border of that surface; and in this respect the gorilla may be said to have the longest heel of nay ape, and a longer heel than man. The head of the astragalus is generally united to its body by a tolerably long neck. This neck is, however, in the gorilla shorter than even in man. The upper surface of this boneis less convex than in man, in Simia, Ateles, and the gorilla; generally; it is more convex than in man. The surface for the externalmalleolus forms, with the upper surface of the astragalus, almost a right angle in Hylobates (as in man), and an obtuse one in Ateles and Lagothrix. In mos tother apes (including Troglodyte) it forms on acuteangle. The angle formed by the upper surface of the astragalus with that for the tibial malleolus, instead of being a right angle, as in man, is generally more or less obtuse, especially in the gorilla. The naviculare has sometimes its tuberositygreatly developed ; this is especially the case in Hylobates. The surfaces for the three cuneiform bones are generally more convex and concave respectively than in man. The ento-cuneiforme generally has its plantar and distal surfaces considerably longer than its dorsal and proximal surfaces respectively. These are exceptionally equal (as in man) in the orang and gorilla. The surface for the hallux is alwaysstrongly convex. The long axis of this articular surface always forms a more or less acute angle with a line drawn across the articular surfaces for the four outer metatarsals. In the lower Simiadoe this angle is as acute as in man In troglodytes it is a little more open, but not nearly so open as is the homotypal angle in the hand even of the same species. The surface is never saddle-shaped in apes. In all apes, even in the chimpanzee, the distal tarsal segment is capable, as a whole, of a considerable degree of motion upon the proximal part, i.e., upon the astragalus and os calcis, and this mobility is extreme in the orang. The absolute longest metatarsal bone is the second of Simia. The metatarsus often exceeds the tarsus in length, but it may, as in the gorilla, fall much short of it, thus resembling man. The four outer metatarsals and the inner mostone diverge instead of being paralle, as in man the former, except in the Simiione and in Ateles, are more rounded than in man, and their distal articular surfaces are less bent downwards, and are limited posteriorly by a deeper transverse groove. The first metatarsal, compared in length with the spine, is longest in Hylobates (10 or 12 to 100), and shortest in Hapale (about 6 to 100). It is always longer than the first metacarpal, except in Simia. Its proximal surface is generally more concave than in man, and its long axis is different. It is as if the metatarsal of man had been removed, softened, and then, after being turned, so that the dorsum looks inwards as well as upwards, reapplied to the convex entocuneiforme, and thus stamped with an oblique depression. The angle formed by this surface, with a line traversing the articular heads of the four outer metatarsals, approximates to a rectangle instead of to a straight line, as in man.
The phalanges are always the same in number as in man, except that the hallux of Simia has often but one. They arevery like their homotypes in the manus, and are convex above, concave and falttened below. Only in the Hapalinoe are the last phalanges laterally compressed instead of flattened. The pedal digits are never nearly so short relatively in apes as they are in man; yet the proportion borne by the hallux, with its metatarsal, to the spine closely approximates in the gorilla to the proportion existing in man, and the proportion is exceeded in Hylobates and Ateles. It is much in defect in Hapalinoe, where it is little more than one-tenth. Its proportion to the whole pes in Hylobates (as in man) is nearly half, while in Simia it is but a quarter, and but little more in the Hapalinoe and the Semnopithecinoe. The hallux, when brought beside the second digit, never reaches so far as in man, but at most (as in chimpanzee) to the proximal end of the second phalanx, or to the middle of the proximal phalanx (as in most Cebidoe), or a little beyond its base (as in Hapale andf the Semnopithecinoe), or not nearly even to the distal end of the metatarsal (as in Simia). Except in Simia and some Cebidoe, notably Hapale, the hallux projects further than does the pollex of the same individual when applied to the second digit of the manus. The hallux also always exceeds the pollex in absolute length, except in Hapale and Simia. The length of the hallux, without its metatarsal, compared with that of the spine, is as 25 to 100 in the chimpanzee (as in man), 19 in the gorilla, and but 8 in Simia. The second digit of the pes is always longer than that of the manus except in the Simiinoe, which so far resemble man. The index digit, with its metatarsal, compared with the spine, is as 38 to 100 in Simia, and it varies thence down to 21 in Cercopithecus. The longest digit of the pes always exceeds that of the manus, except in the Simiinoe and Ateles.
THE MUSCLES
The muscles of apes areverysimilar in number, distribution, an form to those of man, except that in the long-tailed forms (e.g., Semnopithecus) the muscular bundles answering to the coccygeal muscles of man are so greatly developed as to form eight sets of caudal muscles. The latissimus dorsi commonly sends on a slip, called the dorso-epitroclear, as far as the olecranon. Often there is a rhomboideus capitis, and muscle, called levator claviculoe, almost always descends from the cervical transverse processes to the outer part of the clavicle. The flexor longus pollicis and the flexor digitorum profundus are always more or less united. The extensor indivis commonly sends a tendon to the third digit as well as to the index, and at the same time the extensor minimi digiti sends a tendon to the fourth digit as well as to the fifth. An extensor primi internodii pollicis is never developed, but the extensor ossis metacarpi pollicis is often doubled, even in the chimpanzee. In the orang the flexor longus pollicis sends a tendon only to the index. In Hylobates the supinator longus is inserted into the middle of the radius, and there is an anductor tertii internodii indicis going from the metacarpal of the index to its ungual phalanx. Often the extensor brevis pollicis and the abductor longus become more or less united. In spite of the rudimentary condition of the thumb in Ateles, its muscles exist, though in a rudimentary condition, but in Hapale the opponens pollicis is wanting.
The lower limb in the orang generally wants the ligamentum teres, which seems to be sometimes absent in the gorilla also. The glutei muscles of apes are feeble and small, and are inserted low down on the femur. Only in the gorilla are they large enough to cause a small buttock to protrude over the ischiatic tubercosities, but even in this ape the buttocks do not meet so as to conceal the anus. Apes have an extra muscle, called the scansorius, which passes down from the edge of the ilium to the great trochanter of the femur, and must act as a powerful rotator of the thigh inwards. The gracilis is much broader than in man, and is inserted lower down on the tibia than in him, as is also the case with the semi-menranosus and semi-tendinosus. The short head of the biceps femoris is generally wanting. The gastrocnemei and soleus are flatter than in man, and the latter has only a fibular origin. In the lower Simiadoe the plantaris passes over the pulley-like end of the os calcis, and goes to the plantar fascia. No age seems to have any peroneus tertius, but we may find even in Semnopithecus a slender peroneus quinti digiti pasing behind the outer malleolus, and going to the matetarsal of the fifth digit, while in the Cebidoe we may also have a peroneus quarti digiti going similarly to the fourth digit. The tibialis anticus may be divided, as even in the chimpanzee, like its homotype the extensor ossis metacarpi pollicis. The muscles of the foot, with the exception of the interossei, resemble the muscles of the foot of man, and not those of his hand. As regards the interossei even, the difference is very slight. It consists in the insertion of the tendon of that dorsal interosseous mass which is interprosed between and third metatarsals, into the proximal phalanx of the third digit ( as in the human hand), instead of into that of the second digit (as in the human foot). The hallux in the orang is, in spite of its imperfect development, provided with an opponens muscle. The flexor brevis digitorum pedis does not, in apes, arise exclusively from the os calcis, and the flexor accessorius arises from the surface of the deep flexor tendons. The last named muscle may be wanting, as sometimes at least in Hylobates. A muscle, called the abductor ossis metacarpi quinti, exists even in the chimpanzee. In the lower Cebidoe, and especially in the Hapalinoe, the inerossei become true flexores breves, and altogether cease to be visible on the dorsum of the foot.
THE BRAIN
The absolute size of the brain never in any ape approaches that of man. Thus the cranial capacity is never less than 55 cubic inches in any normal human subject, while in the orang and chimpanzee it is but 26 and 27 ¸ cubic inches respectively. The relative size of the brain varies inversely with the size of the whole body, but this is the case in warm-blooded vertebrates generally. The extreme length of the cerebrum never exceeds, as it does in man, two and a quarter times the length of the basi-cranial axis. The proportion borne by the brain to its nerves is less in the apes than in man, as also is that borne by the cerebrum to the cerebellum. In general structure and form the brain of apes greatly resembles that of man. Each half of the cerebrum contains a triradiate lateral ventricle, and though in some Simiadoe the posterior cornu is relatively shorter than in man, it again becomes elongated in the Cebidoe, and in many of the latter it is actually longer relatively than it is in man. The posterior lobes of the cerebrum are almost always so much developed as to cover over the cerebellum, the only exceptions are the strangely different forms, Mycetes and Hylobates syndactylus. In the latter the cerebellum is slightly uncovered, but it is so considerably in the former. In Chrysothrix the posterior lobes are much more largely developed relatively than they are in man. The cerebrum has almost always a convoluted external surface. In this group, however, as in mammals generally, a much-convoluted cerebrum is correlated with a considerable absolute bulk of body. Thus in Hapale (and there only) we find the cerebrum quite smooth, the only groove being that which represents the Sylvian fissure. In Simia and Troglodytes, on the contrary, it is veryrichly convoluted. A hippocampus minor is present in all apes, and in some of the Cebidoe it is much larger relatively than it is in man, and is absolutely larger than the hippocampus major. Of all apes, the orang has the brain which is most like that of man; indeed, it may be said to be like man's in all respects, save that it is much inferior in size and weight, and that the cerebrum is more symmetrically convoluted and less complicated with secondary and tertiary convolutions. If the brain of Simia be compared with that of troglodytes, we find the height of the cerebrum in front greater in proportion in the former than in the latter; also the "bridging convolutions," though small, are still distinguishable , while they are absent in the chimpanzee. Nevertheless, this character cannot be of much importance, since it reappears in Ateles, while two kinds of the genus Cebus (so closely allied as to have been sometimes treated as one species) differ strangely from each other in this respect. The corpus callosum, in apes generally, does not extend so far back as in man, it is very short in Pithecia. In the orang and chimpanee there are, as in man, two corpora albicantia, while in the lower monkeys there is but one. The vermis of the cerebellum is larger in the Cebidoe than in the Simiadoe. In all apes below the Simiinoe, each lateral lobe of the cerebellum gives off a small lobule, which is received into a special fossa of the petrous bone. Certain prominences of the medulla oblongata, termed corpora trapezoidea, which are found in lower mammals, begin to make their appearance in the Cebidoe.
THE TEETH
The teeth of apes consist, as in man, of incisors, canines, premolars, and molars; but the series of teeth no where forms so perfect an arch as in man, the opposite series of grinding teeth tending to become more parallel. No ape has the teeth placed in one uninterrupted series in each jaw, as is the case in the human species, but there is always a small interval (diastema) between each upper canine and the adjacent incisor, and between each lower canine and the adjacent premolar. This condition is due to the excessive size of the canines, the interspaces giving passage to the apices of these teeth. This prolongation of the canines into tusk-like weapons of offence and defence (especially developed in the males), makes a great difference between the aspect of the dentition in apes and man. The number of the teeth is the same as in man in the Simiadoe. The Cebidoe have an additional premolar on each side of each jaw, and the Hapalinoe, besides this, have a true molar the less. The incisors are always nearly vertical save in the Pithecinoe, when their apices project strongly forward. The canines are always considerably longer than the incisors, except in the genus Hapale, where the lower incisors equal the canines in length. The premolars differ structural from the molars much as in man, save that the first lower premolar may be modified in shape to give passage to the upper canine, as is specially to be seen in Cynocephalus. The grinding surface of the molars consists generally of two transverse ridges, each end of each ridge projecting more than the intermediate part, and so giving rise to four tubercles. In Simia and troglodytes, however, we find in the upper molars an additionall structure, which also exists in man. This is a ridge which runs obliquely from the front inner tubercle (or cusp), outwards and backwards to the hind outer tubercle. In the rest of the Simiadoe this ridge is wanting, but it reappears in Ateles and Mycetes amongst the Cebidoe. In the Hapalinoe th etubercles of the molars are more produced and sharp-pointed, in harmony with their decidedly insectivorous habits. The last lower molar may be reduced or much enlarged as compared with the others. Thus is Cercopithecustalapoin it has but three tubercles, while in the Macaci and Cynocephali it is very large, and has five well-developed cusps. The number of milk teeth is as in man, save that the Cebidoe have an additional milk molar. In general the canines are the last teeth to be cut of the permanent dentition. Their cutting sometimes causes such constitutional disturbance as to produce convulsion and death. In the gibbons, however, the canines accompany, if they do not precede, the appearance of the hindmost molar, while in the orang they at least sometimes make their appearance before that grinder.
ORGANS OF NUTRITION AND EXCRETION
The alimentary, circulating, and excretory organs of apes closely resemble those of man. The mouth is always guarded by lips, which, though generally thin, are often very mobile and extensible, the lower lip having no fraenum in the orang, and this is also absent in Cebus, though it may be present in other forms, as e.g., in Troglodytes and cynocephalus.
The tongue is much longer relatively in most apes than in man; but it may closely resemble his, as does that of the orang, in which the circumvallate papillae are collected in a V-shaped aggregation, while there may be only two such papillae, as in cynocephalus and Ateles. In Hylobates the tongue is in this respect man-like; yet in that genus we first meet with a sub-lingual process (which becomes much larger in the lower apes), in the form of a little conical bifid membrane. This structure is formed by the union of the processes upon which open the sub-maxillary ducts-processes much elongated in the chimpanzee, though man-like in the orang.
The uvula is generally present, but becomes rudimentary in the Cebidoe generally, though it exists as a relatively thick, short structure in Hapale. It is long and pointed in Semnopitchecus, and and plainly visible in Hylobates and Troglodytes. On the other hand, in Simia it is disguised by the extensive development of the membranous edge of the velum palati on each side of it.
The stomach is simple in all the apes except the semnopithecinoe. It is especially human in shape in Hylobates, except that the pylorus is somewhat more elongated and distinct. It is of a rounded form in Pitchecia, and in Hapale the cardiac orifice is exceptionally near to the pylorus. In the Semnopithecinoe the stomach is extremely sacculated, especially at the cardiac end, being, in fact, very like a colon spirally coiled. It is in the stomach of these apes that the oriental Bezoar stones are found.
The intestine in apes is devoid of valvuloe connicentes, but is always provided with a well-developed coecum, though it is short and conical in Cynocephalus. Only in the Simiinoe do we find a vermiform appendix.
The colon may be much longer relatively than in man, as in Simia and Troglodytes. It may be greatly sacculated, as in Hylobates; or devoid of sacculations, as in Cebus. As in foetal man, so in the lower apes, only the right extremity of the mesocolon is involved in the formation of the great omentum, the middle and left parts of the mesocolon lying behind, and independent of the omentum. This is not, however, the case in the Simiinoe which are more like adult man in this respect.
The liver may be very like man'sespecially in Hylobates, the orang, and the chimpanzee; but in the gorilla both the right and left lobes are cleft by a fissure almost as much as in Cynocephalus. In the Semnopithecinoe the liver is much divided, and it is placed obliquely to accommodate the sacculated stomach. The lateral lobes of the liver are in Hapale very much larger than the central lobe. The caudatelobe is very large in the cebidoe, especially in Ateles, and above all in Pithecia. There is always a gallbladder.
The larynx is in many apes furnished with sac-like appendages. These are different in different species as regards number, size and situation. They may be dilatations of the laryngeal ventrice (opening into the larynx below the false vocal chords), as in Simia and Troglodytes. They may open above the false vocal chords so as to be, in fact, extensions of the thyro-hyoid membrane, as in Hylobates. There may be but a single median opening in the front part of that membrane at the base of the epiglottis, as in the Simidoe below the Simiinoe. There may be a single median opening at the back of the trachea, just below the cricoid cartilage, as in Ateles. There may be but a single sac, or there may be five, as sometimes in Mycetes. These may be enormous, meeting in the middle line in front, and extending down to the axillae, as in the gorilla and orang. A sac may occupy the cavity of the expanded body of the hyoid bone, as in Mycetes.
The os hyoids has its basilar part generally somewhat more convex and enlarged than in man; but in Mycetes it becomes greatly enlarged and deeply excavated, so as to form a great bony baldder-like structure.
The cornua of the hyoid are never entirely absent, but the anterior or lesser cornua may be so, as in Mycetes. The anterior cornua never exceed the posterior cornua in length; but they may be 9e.g., in Cercopithecus) more largely developed relatively than in man, and they may even be jointed structure, as in Lagothrix.
The lungs have generally the form of those of man; but the right lung may have four lobes, as, e.g., in Hylobates.
The great arterial trunks in Simia and troglodytes are arranged as in man. In Hylobates and the lower apes, however, the left carotid may take its origin from the innominate artery.
THE GENERATIVE ORGANS
The generative organs are in common with the other parts of the body, formed on the same model as in the human species. The penis is pendulous, i.e., hangs freely, instead of being (as in the dog) bound to the ventral surface of the abdomen. The prepuce, however, is without a fraenum. The testes are relatively large, and descend into a scrotum. In some species, however, they do not descend so much as they do in man, but remain just outside the inguinal ring, and are thus placed rather beside than beneath the penis. These parts, as has been said, are brightly coloured in some of the lower Simiadoe. The penis is furnished with a bone in all the apes below the Anthropoid ones, and probably in the latter also, since the chimpanzee has one about one-third of an inch long and gristly at each end. In all apes the uterus is single, and not two horned; but it is more elongatedrelativelyin monkeys than in the human species. The clitoris is well-developed, but boneless in the Simiadoe, and is large even in Troglodytes niger. In the Cebidoe it contains a bone; and in some genera, especially in the cebinoe, it is enormously developed, so as to be very easily mistaken for a penis. In Ateles, however, its length is mainly due to its extremely elongated prepuce.
The placenta of apes is discoidal an deciduate, and is generally bilobed. Sometimes, however, as in Mycetes, it is single. It is especially thick in proportion in the Hapalinoe. In the Simiadoe there is but one umbilical vein, but in the Cebidoe there are two.
Gestation in the lower Simiadoe lasts about seven months, but in the Hapalinoe only three months.
Menstrustion occurs periodically, but the excretion is less sanguineous than in the human species. In the lower Simiadoe it is chiefly manifested by a turgescence of the external organs, which may extend widely in the parts adjacent, and even beneath the tail.
Lactation lasts, in the better known forms, for an average of six months, and the young are carried at the breast in a very human attitude.
Read the rest of this article:
(1) Ape: Introduction, General
(2) Apes - Anatomy (YOU ARE HERE)
(3) Apes - Distribution in Time, Geographical Distribution, Zoological Position and Affinities