Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/175

Rh SKELETON.] APE 161 and corcicoid processes are short in the lower Simiada; ; both are long in the Simiince 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 Cebidai it may be less than 12 to 100. This bone is exceptionally slender in Mycetes, and is broadest in Troglo dytes and the C ijnopithecince. In the lower Simiadce a fossa is excavated beneath the acromial end of the bone. Ixarely, as in Simla, 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 SO 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 Simiince. The tuberosities may project upwards slightly above the articular head, as in Cynocephalus. Generally they are about on a level with its top, but may be decidedly below it, as in Ateles, Hylobates, and Simla. The radial border of the bicipital groove may be very prominent, as in Cynocephalus. The groove may be spanned by a bridge of bone, as sometimes in the chimpanzee. The position of the nutrient foramen varies even in different individuals. The supinator ridge is especially developed in Cynocephalus, Cebus, and llapale. In the Simiince it is only slightly developed. The external condyle is distinct in the Simiince; in the other genera it is closely applied to the capitellum. A supra-condyloid foramen is never present normally in the Simiadce, but is present more or less constantly in the Cebidce, from Cebus downwards, being perhaps most fre quently 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 Simiince and llapale. It almost disappears in the Cyno- pithecince. The radius and ulna are never ankylosed 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 fre quently falls short 01, than exceeds, that of the humerus. It exceeds it in Simia, Hylobates, Ateles, Cynocephakis, and sometimes in the Semnojnthccince. 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 stoutest in Cynocephalus, slenderest in Ateles, and, above all, in Hylobates. The ulna varies, like the radius, in length and breadth. The olccranon is broad in the Simiina, but in the lower apes it is relatively larger, especially in Cynocephalus and Mycetes. The styloid pro cess is very long in Hylobates, where it develops a pro minence, 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 a 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 docs 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 Simiadce, 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 Ateles; it is very large in the gorilla and Cyno- cepJialus, and long but slender in Hylobates. Commonly it contributes to form, with the cuneiforme, a cup for the reception 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 Simiadce the concavity is sometimes present, and some times in the Cebidce (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 rudi mentary 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 Simiadce 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, contri butes 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 nar rower 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 llapalince, the ultimate phalanges are always flattened from dorsum to palm. In the HapaliiUB they are laterally com pressed, curved, and pointed to support the peculiar claws of that sub-family. The length of the pollex with its meta carpal bears a much greater proportion to that of the spine in 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 (viz., as 17 to 100) in Hylo bates, and longest (viz., as 32 to 100) in llapale. The pollex, when brought beside the index digit, rarely extends so far as in man, and does so only in the Cebidce, where, in the Hapalince, it may reach nearly to the distal end of the proximal phalanx of the index. In Cyno cephalus it may reach the middle of that phalanx, while ill