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  Section: Anatomy of Vertebrate Animals » The Classification and Organization of the Mammalia
 
 
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The Anthropomorpha

 
     
 

b. The Anthropomorpha differ from the Cynomorpha in the following characters: They are especially arboreal animals, which habitually assume a semi-erect posture, supporting the weight of the fore-part of the body upon the ends of the fingers, or, more usually, upon the knuckles. There is no tail. The thigh and the leg are, respectively, shorter than the arm and the fore-arm. The dorso-lumbar vertebrae are seventeen or eighteen in number, and their spines are not inclined toward a common point. They develop no interlocking mammillary and accessory processes. The sacrum contains more than three anchylosed vertebrae. The thorax is rather broad than laterally compressed, and the sternum is flattened from before backward, and wide. The axis of the head of the humerus is directed more inward than backward, and the upper part of the shaft is not bent as in the Cynomorpha. The radius is capable of complete pronation and supination.

The relative proportions of the incisor teeth are the same as in Man; that is to say, the inner upper incisors and the outer lower incisors are larger than the others. The crowns of the upper and lower molars have the same patterns as those of Man.

The caudal muscles are small or absent. When the pollex has a flexor tendon, that tendon is not a slip given off from one common to the flexor pollicis and flexor perforans, as in the Cynomorpha. The plantaris does not pass over a pulley furnished by the calcaneal process, as in the Cynomorpha; and the flexor brevis has an origin from that process. The peronoeus quinti digiti has not been observed.

There are three well-marked genera of Anthropomorpha- Hylobates, Pithecus, and Troglodytes; and perhaps a fourth, Gorilla, may be advantageously separated from the lastnamed.

Pithecus, the Orang, has the smallest distributional area, being confined to the islands of Borneo and Sumatra; Hylobates, the Gibbons, of which there are several species, is found over a considerable area of Eastern Asia and the islands of the Malay Archipelago. The Chimpanzee and Gorilla are met with only in the intertropical parts of West Africa.

The Gibbons are those Anthropomorpha which are most nearly allied to the Cynomorpha. They possess ischial callosities, and the nails of the pollux and hallux, only, are broad and flat. The arms are so long that the points of the fingers readily touch the ground when the animal stands upright, as it very readily and commonly does. The Gibbons also run with great swiftness, putting the sole of the foot flat on the ground and balancing themselves with their long arms.
Nevertheless, they are essentially arboreal animals, leaping from bough to bough of the trees in the forests which they frequent with marvellous force and precision. The manus is longer than the pes, and the antibrachium considerably longer than the brachium. The Gibbons do not exceed three feet in height; their heads are small, and their bodies and limbs remarkably slender.

None of the other Anthropomorpha have callosities, and the nails of all the digits are flattened. They are all heavier in make, with proportionally shorter limbs and larger heads than the Gibbons. In the Orangs, which rarely attain a stature of more than four feet and a half, the arms are very long, their span, when outstretched, being nearly double the height of the animal. The brachium and the antibrachium are equal in length. The long and narrow pes is longer than the equally narrow manus, and the sole cannot be placed flat upon the ground, but the animal rests upon the outer edge of the foot when it assumes the erect posture. This posture, however, ia quite unnatural, and the Orangs cannot run as the Gibbons do, but swing themselves along upon their long arms, as it were upon crutches.

The pollex and the hallux are both short, the latter remarkably so; and the hallux is not uncommonly devoid of a nail. The palmar and plantar aspects of the digits are naturally concave, and they cannot be completely straightened.

The Chimpanzee attains a stature somewhat greater than that of the average Orang. The span of the arms is about half as much again as the height. The antibrachium is about as long as the brachium. The manus is equal to, or a little longer than, the pes; and these parts of the limbs are not so elongated, or so curved, as the corresponding parts of the Orang. The sole can be readily placed flat upon the ground, and the Chimpanzee easily stands or runs erect. But his favorite attitude is leaning forward and supporting himself on the knuckles of the manus. Both the hallux and the pollex are well developed and possess nails.

The Gorilla exceeds five feet in height and may reach five feet six inches. The span is to the height as about three to two. The brachium is much longer than the antibrachium. The pes is longer than the manus, and both are much broader than in the other Anthropomorpha. In consequence of this circumstance and of the greater development of the heel, the erect posture is easily maintained, but the ordinary attitude is the same as that assumed by the Chimpanzee. The hallux and the pollex have well-developed nails. The basal phalanges of the three middle digits of the foot are bound together by the integument.

With respect to the skeleton in the Anthropomorpha, the Gibbons have the spinal column nearly straight, with a very open vertebro-sacral angle. In the Orangs the dorso-lumbar vetebrae form a curve, which is nearly as much concave forward as in a new-bom child. In the Chimpanzee the spinal column begins to exhibit the curvatures which are characteristic of the adult human subject; and these are still more marked in the Gorilla.

The spinous process of the second cervical vertebra is bifurcated in the Chimpanzee, but this human character does not appear in the others.

In the Gibbons there are usually eighteen dorso-lumbar vertebrae; but in the other Anthropomorpha the number is ordinarily seventeen, as in Man, or may be reduced to sixteen. The Orang has the human number of twelve pairs of ribs, but the Chimpanzee and Gorilla have thirteen, and the Gibbons may possess fourteen pairs of ribs. The thorax is wide, and the sternum broad and flat. In the Orang it may ossify from a double longitudinal series of centres, as sometimes happens in Man.

In the Gibbons the transverse processes of the last lumbar vertebra are not exceptionally broad, and do not unite with the ilia. But in both the Chimpanzee and Gorilla they are wide, and become more or less closely connected with the ilia. The last lumbar vertebra may become anchylosed with the sacrum in the Gorilla. All these conditions of the last lumbar vertebra are occasionally met with in Man.

The sacrum is broad, and contains not fewer than five anchylosed vertebrae, but its length always exceeds its breadth (whereas its breadth is equal to, or exceeds, its length, in Man), and its anterior curvature is but slight. The short coccyx is made up of not more than four or five vertebrae. In the skull, the proper form of the brain-case is always more or less disguised in the adult males, by the development of crests for muscular attachment, or of the orbits and the supraorbital ridges. In the Gibbons and Chimpanzees, the latter are large, but the sagittal crest is absent, and the lambdoidal small. In the Orang, the brow-ridges are small, so that the true form of the forehead is seen better than in the other Apes, but the sagittal and lambdoidal crests are strong. In the old male Gorilla the sagittal and lambdoidal crests, and the supraorbital ridges, are alike enormous. The frontal sinuses are large, and extend into the brow-ridges both in the Gorilla and Chimpanzee. The jaws are largest in proportion to the brain-case in the Gorilla and the Orang; smallest in some varieties of Chimpanzee.

In all the Anthropomorpha the transverse is much less than the longitudinal diameter of the cranial cavity. The roofs of the orbits project into the frontal portion of the braincase, and diminish its capacity by causing its floor to slope from the middle line obliquely upward and outward. The occipital foramen is situated in the posterior third of the base of the skull, and looks obliquely backward and downward. The frontals meet in the base of the skull over the ethmopresphenoidal suture in the Gibbons and in the Gorilla, as in the Baboons; but not in the Chimpanzee or the Orang. The alisphenoids unite suturally with the parietals, as is the rule in Man, in the Gibbons and (usually) in the Orangs; but, in the Chimpanzee, the squamosal unites with the frontal and separates the alisphenoid from the parietal, as happens, exceptionally, in Man. The nasal bones are flat and early anohylosed together, in the Gibbons, Orangs, and Chimpanzees. In the Gorilla the nasal bones are distinctly convex from side to side, and rise above the level of the face. None of these Apes have a spina nasalis anterior; and, only in the Siamang, is there a rudiment of the mental prominence in the mandible. The premaxillo-maxillary suture persists beyond the completion of the second dentition in all but the Chimpanzee, in which it disappears before that period. The epiotic region is never developed into a distinct mastoid process; and there is an ossified styloid process only occasionally in the Orangs. The palate is long and narrow, the alveolar margins being nearly parallel, or even diverging anteriorly. The zygomatic arches are strong, wide, and curved in two directions.

The proportion of the length of the basi-cranial axis to that of the cerebral cavity does not fall lower than the ratio of 10 to 17 in any of the Anthropomorpha.

The body of the hyoid approaches the form of that of Man most nearly in the Orang. In the other genera it is more excavated posteriorly.

The scapula of the Orang is most like that of Man, especially in the proportion of the supra-and infra-spinous fossae, in the proportional length of the anterior and the posterior borders, and in the angle made by the spine with the vertebral margin. In the other genera the posterior border is longer in proportion than in Man, and the spine of the scapula cuts the vertebral margin more obliquely. After the Orang's, the scapula of the Gorilla comes nearest to that of Man.

On the other hand, the long and straight clavicle of the Orang is least like that of Man.

The head of the humerus loses the backward inclination which it has in the lower Apes, and becomes directed upward and inward, as in Man. The radius and ulna are curved, and leave a wide interosseous space. There are nine bones in the carpus in both Hylobates and Pithecus, but only eight in the Chimpanzee and Gorilla. In Hylobates the articular surface presented by the trapezium for the pollex is almost globular. It is evenly convex in the Chimpanzee; but, in the Gorilla, it has the characteristically human saddle shape. The pollex is longest and strongest in proportion in Hylobates; its length in proportion to that of the manus being in H. syndactylus as three to seven. In the Gorilla, the pollex has rather more than one-third the length of the manus; in the Orang and Chimpanzee it has about one-third the length of the manus.

The pelvis differs but little from that of the Cynomorpha in Hylobates. In the other genera the pelvis is still elongated. The antero-posterior diameter of the brim of the pelvis greatly exceeds the transverse, the tuberosities of the ischia are strongly everted, and the pubic symphysis is very long, the arch being correspondingly reduced; but the ilia are wider and more concave forward in the Chimpanzee than in the Orang, and in the Gorilla than in either.

In the female Chimpanzee, which is of about the same size as the male, the dimensions of the basin of the pelvis, and, of its outlets, are greater than in the male, though the general form and absolute length of the pelvis are the same in the two sexes. The female Gorilla is much smaller than the male, and the pelvis is shorter in proportion, but the intersciatic measurement of the outlet is absolutely as great as in the male, and the transverse diameter of the brim is nearly as great. As, at the same time, the antero-posterior diameter is much shorter, the brim of the pelvis of the female is much more round. The female Orangs, also, are smaller than the males. The basin of the pelvis is relatively, but not absolutely, larger in all its dimensions, and the brim rounder.

The femur of the Orang has no round ligament, and differs in this respect from the same bone in the other Anthropomorpha. The femur of the Gorilla resembles that of Man, most especially in the projection of the articular surface of the inner condyle beyond the outer.

The length of the whole foot to that of the tarsus is in Hylobates, as thirty-five to ten, and the proportion is about the same in the Orang; in the Chimpanzee it is as twentyfour to ten; and, in the Gorilla, about the same (twenty-three to ten in the specimen measured).

The hallux has not more than one-fourth of the length of the foot in the Orang; in the Gorilla less than five-twelfths in the Chimpanzee and in Hylobates a little more.

In the second digit of the pes of the Orang and the Chimpanzee, the phalanges, taken together, are longer than the metatarsal bone of the digit; in the Gorilla, they are about equal in length to the metatarsal. The calcaneal process is longest, strongest, and broadest, in the Gorilla. In the astragalus the articular surface for the tibia is broadest in the Gorilla; but, in this Ape, as in the others, it is inclined a little inward when the foot is in its natural position; and the surface for the external malleolus is oblique, and looks upward as well as outward.

It is a mistake, however, to suppose that the disposition of these surfaces has any thing to do with the more or less marked tendency of the plantar surface to turn inward, and of the outer edge of the pes to be directed downward, which is observable in all the Anthropomorpha. This tendency is the result of the free articulation between the scaphoid and the cuboid, on the one hand, and the astragalus and the calcaneum on the other; the consequence of which is, that the distal portion of the pes, with the first-mentioned bone, being pulled by the tibialis anticus, easily rotates round its own axis, upon the surface presented by the astragalus and calcaneum. This ready inversion of the sole must as much facilitate climbing, as it must interfere with the steadiness of the foot in walking.

The distal surface of the ento-cuneiform is much inclined inward in all the Anthropomorpha and is convex from side to side, or subcylindrical. The metatarsal bone of the hallux presents a corresponding articular concavity to this surface, and has a great range of motion in adduction and abduction. The inward inclination of the articular facet of the ento-cuneiform, and its consequent separation from the facet upon the mcsocuneiform for the second digit, is greatest in the Orang, in which the hallux is habitually directed at right angles to the long axis of the foot. The distal phalanx of the hallux is not unfrequently absent in the Orang.

All the Anthropomorpha possess certain muscles which are not usually found in Man, though they may occur as varieties in the human subject. These are the levator claviculae, the dorso-epitrochlearis, the scansorius(Not actually described in the Gorilla, and absent in some Cbimpanzees.) and the abductor ossis metacarpi quinti digiti. They are also devoid of two muscles which are usually present in Man-the extensor primi internodii pollicis(The former muscle is said to be present by several anatomists in the Chimpanzee and other Apes; but what they have taken for it is the metacarpal division of the extensor ossis metacarpi.) and the peronoeus tertius. The former of these is sometimes, and the latter frequently, wanting in the human subject.

The flexor accessorius appears to be regularly absent in Hylobates and Pithecus, and, in the majority of cases, in the Chimpanzee. The transversus pedis seems to be absent in the Orang, but it is present in the other Anthropomorpha.

Many muscles which exist both in these Apes and in Man have different origins in the former. Thus, the soloeus has only a fibular head, and takes no origin from the tibia. The flexor brevis digitorum pedis never arises altogether from the calcaneum, but a large proportion of its fibres spring from the tendons of the deep flexors. The calcaneal head furnishes the tendons for the second, or the second and third, digits. The interosseous muscle which lies on the tibial side of the middle digit of the pes, usually arises from the fibular side of the second metatarsal as well as from the tibial side of its own metatarsal, and its origin lies on the dorsal side of that of the fibular interosseous muscle of the second digit. Hence, of the socalled dorsal interossei (or interossei which are visible on the dorsal aspect of the pes) two belong to the middle digit, and one, to the second and fourth digits respectively; which is the same arrangement as that which obtains in the manus. The flexor pollicis is more or less closely connected with the flexor communis perforans, or with that part of the muscle which goes to the index digit. The connection is slightest in Hylobates, the origins of the two muscles, only, being united. It is most extensive in the Orang, in which no tendon goes to the pollex. The same complete loss of the flexor pollicis, as a thumb-muscle, occasionally takes place in the Gorilla; but in this animal, as in the Chimpanzee, the rule appears to be, that the flexor pollicis unites at its origin with part of the flexor perforans, and that the fleshy fibres converge to a common tendon which divides into two, one for the pollex and the other for the index. In Hylobates, the short head of the biceps brachii arises from the pectoralis major, and the adductor hallucis and transversus pedis form but one muscle.

The flexor longus hallucis takes an origin from the external condyle of the femur in the Orang; and the pectoralis major arises by three distinct slips.

Some of the muscles in the Anthropomorpha differ in their insertion, or in the extent to which they are subdivided, from what is usual in the corresponding muscles of Man. Thus the extensor ossis metacarpi pollicis ends in two distinct tendons one for the trapezium, and the other for the base of the metacarpal bone of the pollex. That part of the tibialis anticus which goes to the metatarsal of the hallux is usually very distinct, and is sometimes reckoned as a separate muscle, the abductor longus hallucis.

In the Gibbons and in the Orang, there is a complete set of deep extensors for the four ulnar digits, the tendons of the extensor indicis and extensor minimi digiti subdividing to supply the third and fourth digits.

In the Gorilla and Chimpanzee each of these muscles have but a single tendon, as is the usual arrangement in Man.

The interossei of the hand are each divided into two muscles with distinct tendons-a flexor brevis primi internodii and an extensor brevis tertii internodii. The division is less obvious in the Orang than in the other Anthropomorpha.

In Hylobates, the tendon of the flexor perforans pedis goes only to the fifth digit, and is not directly connected with that of the flexor longus hallucis, which supplies the other four digits. In the Orang, also, the tendons of the two muscles are separate; but the flexor perforans suppHes the second and the fifth digits, and the flexor hallucis the third and fourth. It gives no tendon to the hallux. In both the Chimpanzee and the Gorilla, a very large tendon is given to the hallux by the flexor hallucis, and it also supplies the third and fourth digits. The tendon of flexor longus digitorum is but slightly connected with that of flexor hallucis, and its divisions go to the second and fifth toes. In both the manus and the pes of Hylobates a muscle occurs which is not, at present, known in any other Mammal. It arises from the second metacarpal or metatarsal bone, and is inserted by a long tendon into the preaxial side of the ungual phalanx of the second digit; it may be termed "abductor tertii internodii seaundi digiti."

The Orang, in like manner, stands alone in possessing a small but distinct opponens hallucis. (It must be borne in mind that these statements respecting the myology of the Anthropomorpha are based upon my own dissections (sometimes supplemented by those of Duvernoy and other anatomists) of particular specimens. Endless varieties will no doubt be met with by those who carry their inquiries further.)

The volume of the brain, in the Orang and in the Chimpanzee, is about twenty-six or twenty-seven cubic inches; or about half the minimum size of a normal human brain. In the Gorilla, the volume rises to near thirty-five cubic inches. In the Gibbons the brain is very much smaller; and the Siamang, among these, is remarkable for the short posterior lobes of the cerebrum, which, in this anthropomorphous Ape, do not overlap the cerebellum as they do in all the others.

The cerebral hemispheres are higher in proportion to their length in the Orang than in the other Anthropomorpha; but, in all, they are elongated and depressed, as compared with those of Man. The frontal lobes taper off anteriorly, and their inferior surfaces are excavated from without downward and inward, in correspondence with the projection of the upwardly convex roofs of the orbits into the cranial cavity. The posterior cornu of the lateral ventricle is always well developed, and contains a prominent hippocampus minor and emicentia collateralis. An occipito-temporal or "external perpendicular" sulcus is always present. It is most nearly obliterated in the Orangs. All the gyri of the human brain are represented in the cerebral hemispheres of the Chimpanzee; but they are simpler and more symmetrical, and larger in proportion to the brain (see Figs. 21 and 22). The fissure of Sylvins is less inclined backward, and that of Rolando is placed more forward than in Man. The insula has simpler and fewer radiating sulci, and is not completely hidden by the temporal lobe. Only the second, third, and fourth annectent gyri appear upon the surface. The first remains folded upon itself, and gives rise to the characteristically simian occipito-temporal or external perpendicular sulcus. The occipito-parietal sulcus, on the inner face of the hemisphere, is much more nearly perpendicular than in the human brain. The corpus callosum is relatively smaller; the septum lucidum is very thick, and the precommissural fibres are well developed. The vermis is small in proportion to the lateral lobes of the cerebellum, and the flocculi are relatively small, and lie below the latter.

The whole cerebellum is larger in proportion to the cerebral hemispheres; the latter being to the former, as 8 1/2 to 1 in Man, but as 5 3/4 to 1 in the Chimpanzee. (It must be recollected that the brains of young anthropomorphous Apes, only, have been examined. Perhaps this has to do with the absence of mineral deposits in the pineal gland of the Apes.) The nerves are larger in proportion to the brain than in Man. There are no corpora trapezoidea, such as exist in the lower Mammals, and the corpora albicantia are double.

In all the Anthropomorpha, the inner incisors are larger than the outer, in the upper jaw; smaller in the lower jaw. There is a diastema, though it is often but small in the female Chimpanzees. The canines are large and strong, and may be grooved longitudinally on their inner sides. The premolars have three roots in the upper jaw, two in the lower. The crowns of the middle molars, above, have four cusps, and an oblique ridge which extends from the antero-external to the postero-iaternal cusp; and those of the middle molar, below, have five cusps, as in Man. The crown of the anterior premolar in the lower jaw is pointed, and has a long, sharp, oblique anterior edge as in the Cynomorpha.

In the Gibbons, the permanent canine emerges contemporaneously with, or before, the last molar; but, in the other Anthropomorpha, the last permanent canine is cut, ordinarily, only after the appearance of the last molar.

In the Orang the circumvallate papillae of the tongue are arranged in a V, as in Man. In the Chimpanzee they are disposed like a T, with the top turned forward. The Chimpanzee and the Siamang have a uvula, but the Orang has none. The stomach of the Chimpanzee is very like that of Man; but in the Orang the organ is more elongated, with a round cardiac and more tubular pyloric portion. An appendix vermiformis is found in the caecum of all four genera. In the Chimpanzee and Gorilla, the origin of the great arteries from the arch of the aorta takes place as in Man. In the Orang, they are sometimes disposed as in Man; while in other specimens the left carotid comes off from the innominata, and only the subclavian of the left side arises directly from the aorta. In Hylobates, the latter arrangement appears to obtain.

The kidney has only a single papilla in Hylobates and Pithecus.

Only one species of Hylobates, namely, the Siamang, is known to possess a laryngeal sac. This is globular, and communicates by two apertures, situated in the thyro-hyoid membrane, with the larynx. In the Orang, Chimpanzee, and Gorilla, enormous air-sacs result from the dilatation of the lateral ventricles of the larynx. These dilatations extend down, in front of the throat, on to the thorax and even into the axillae, and sometimes open into one another in the middle line.

In the adult male Chimpanzee the penis is small and slender, and terminates in a narrow and elongated glans. The testes are very large, and the communication between the tunica vaginalis and the peritonaeum is completely closed. The glans penis of the Gorilla is button-shaped. In the Orang it is cylindrical, and the testes are situated close to the inguinal canal, which has been found open on one side, and closed on the other. An os penis is developed in the males.

The females have the clitoris large, and the uterus, which is undivided into cornua, resembles that of the human subject. The placenta of a Chimpanzee foetus, 11 1/2 inches long, was simple, rounded, 3 1/2 inches in diameter, and 0.6 inch thick in the centre. The umbilical cord was inserted near one of its edges.

The proportions of the limbs to one another and to the body do not sensibly change after birth; but the body, limbs, and jaws, enlarge to a much greater extent than the brain-case.

The amount of variation in the characters of the skull among the Chimpanzees, Gorillas, and Orangs, is exceedingly remarkable, especially if taken in connection with their very limited areas of distribution.

Of the four genera of the Anthropomorpha, the Gibbons are obviously most remote from Man, and nearest to the Cynopithecini.

The Orangs come nearest to Man in the number of the ribs, the form of the cerebral hemispheres, the diminution of the occipito-temporal sulcus of the brain, and the ossified styloid process; but they differ from him much more widely in other respects, and especially in the limbs, than the Gorilla and the Chimpanzee do.

The Chimpanzee approaches Man most closely in the character of its cranium, its dentition, and the proportional size of the arms.

The Gorilla, on the other hand, is more Man-like in the proportions of the leg to the body, and of the foot to the hand; further, in the size of the heel, the curvature of the spine, the form of the pelvis, and the absolute capacity of the cranium.

 
     
 
 
     



     
 
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