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(Part 22)

(C) The Anatomy of Apes (cont.)

Ape Skeleton - Appendicular Skeleton (cont.): Foot; Phallanges (Toes).

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 Simiadae, 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 calcis 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 Simiadae, 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 external malleolus 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 most other apes (including Troglodytes) it forms on acute angle. 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 tuberosity greatly 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 always strongly 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 Simiadae 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 Simiinae 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 ento-cuneiforme, 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 Hapalinae 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 Hapalinae, 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 Hapalinae and the Semnopithecinae. 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 Cebidae), or a little beyond its base (as in Hapale andf the Semnopithecinae), or not nearly even to the distal end of the metatarsal (as in Simia). Except in Simia and some Cebidae, 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 Simiinae, 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 Simiinae and Ateles.

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