Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/177

Rh SKELETON, MUSCLES.] APE 163 arch. In no ape, however, do the distal ends of the inner metatarsals form the anterior point of siipport of the antero- posterior 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 down wards, or both, and is concave or grooved behind, except in the gorilla. In no ape are the long axis of the heel or the pcroneal and tibial surfaces of the os calcis so vertical as they are in man j 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 Pitheda, and not great in Aides and Hylobates. It is more marked in the lower Simiadce, 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 any 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 bone is 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 an 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 Simiadce 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 absolutely longest mctatarsal 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 resem bling man. The four outer metatarsals and the inner most one diverge instead of being parallel, as in man. The former, except in the Simiince and in Ateles, are more rounded than in man, and their distal articular surfaces are less bent downwards, and arc limited poste riorly 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 ir.wards 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, approxi mates 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 are very like their homotypes in the manus, and are convex above, concave and flattened below. Only in the Hapalince 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 pro portion 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 Hylo bates and Ateles. It is much in defect in Hapalince, 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 Hapalince and the Semnopithecince. The hallux, when brought beside the second digit, never reaches so far as in man, but at most (as in the chimpanzee) to the proximal end of the second phalanx, or to the middle of the proximal phalanx (as in most Cebidce), or a little beyond its base (as in Hapale and the Semnopithecince}, or not nearly even to the distal end of the metatarsal (as in Simia}. Except in Simia and some Cebidce, notably Hapale, the hallux pro jects 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 Simiince, 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 Simiince and Ateles. THE MUSCLES. The muscles of apes are veiy similar in number, dis tribution, and 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- epitrochlear, as far as the olecranon. Often there is a rhomboideus capitis, and a muscle, called levator claviculce, almost always descends from the cervical transverse pro cesses to the outer part of the clavicle. The flexor longus pollicis and the flexor digitoriim profundus are always more or less united. The extensor indicis 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 2^ollicis is never developed, but the extensor ossis metacarpi pollicis is often doubled, even in the chim panzee. In the orang the flexor longus pollicis sends a tendon only to the index. In Hylobates the siipinator longus is inserted into the middle of the radius, and there is an abductor tertii internodii indicis going from the meta carpal 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 rudi mentary condition, but in Hapale the opponens pollicis is wanting. The lower limb in the orang generally wants the