THE CHIMPANZEES AND ORANGS. 7 
communis from that for the extensor internodii pollicis: this second ridge gives a 
trihedral shape to the shaft, the outer and hinder surface being rather convex, the inner 
one flat, the anterior one becoming rather concave as the bone expands to its distal end. 
In the radius of the skeleton of the male Gorilla in the Museum of the Royal College 
of Surgeons (PI. IV. fig. 1), the distal epiphysis was wanting, and the description is 
taken from that of the older individual in the British Museum (Pls. XII. & XIII. 
fig. 2). 
The process called ‘ styloid’ in the Human radius is less produced than in Man, and 
is represented rather by a large rough prominence above the radial or outer angle of the 
articular surface for the scaphoid. This prominence gives a proportionally larger surface 
than in Man for the insertion of the tendon of the ‘supinator longus.’ It is not im- 
pressed, behind or externally, so deeply by the two grooves for the extensor muscles of 
the metacarpal and first phalangeal bones of the thumb; those grooves, indeed, are 
scarcely marked’in the Gorilla; the common shallow depression for them is separated 
by a short tuberosity from the grooves for the extensores carpi radiales. A still stronger 
tuberosity, pretty equally bisecting the posterior surface of the distal expansion of the 
radius, and in which the posterior ridge of the radial shaft terminates, divides the fossa 
for the radial extensors of the wrist, from the wider and deeper one for the strong tendons 
of the extensor communis digitorum. The semicircular depression for the lower end of 
the ulna is well marked: the distal articular surface is divided, as in Man, by two 
concave facets, the larger one for the os scaphoides, the lesser for the os lunare: the 
anterior border of the latter is much produced, giving a greater proportional antero- 
posterior extent to the ‘lunar’ surface than in Man. The orifice for the ‘arteria 
medullaris’ (Pl. IV. fig. 1, 7) is situated as in Man, and the direction of the canal 
is ‘ proximad’ or towards the elbow-joint. It may be noted that the hair covering the 
arm and fore-arm has a direction corresponding with that of the medullary arteries of 
the brachial and antibrachial bones. 
The first and most significant difference presented by the radius of the Chimpanzee 
(Pl. IV. fig. 3), as compared with that of the Gorilla, is its equality of length with 
the humerus of the same limb; a less important difference is the greater projection of 
the margin of the upper articular end over the neck ; in both of which it departs further 
from the Human type. In the greater relative thickness and longitudinal outward 
curvature of the shaft, it corresponds with the radius of the Gorilla. On the back part 
of the distal expansion of the bone (ib. fig. 5), the letter / marks the groove for the ex- 
tensor carpi radialis longior ; m that for the extensor carpi radialis brevior ; n, o mark the 
depression for the tendons of the extensor digitorum communis, in which may be 
discerned an oblique groove for the extensor secundi internodii pollicis, better marked 
than in the Gorilla. 
The characteristics of the Human radius (Pl. IV. figs. 7-10), as educed by the 
foregoing observations, are,—first, its greater shortness relative to the humerus (seldom 
