(C) The Anatomy of Apes (cont.)
Ape Skeleton - Appendicular Skeleton: Hand; Phallanges (Fingers).
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 Simiadae, 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 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 Simiadae the concavity is sometimes present, and sometimes in the Cebidae (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 Simiadae 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 Hapalinae, the ultimate phalanges are always flattened from dorsum to palm. In the Hapalinae 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 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 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 Cebidae, where, in the Hapalinae, 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.
Read the rest of this article:
Ape - Table of Contents