548 ANATOMY OF VERTEBEATES. 



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 propor- 

 tional antero-posterior extent to the ' lunar ' surface than in Man. 

 The orifice for the ' arteria meduUaris ' is situated as in Man, 

 and the direction of the canal is ' proximad ' or towards the elbow- 

 joint.^ The shaft of the ulna, 55, presents two slight opposite 

 curves, the upper one concave, the lower one convex, on the 

 ulnar or inner aspect. Viewed sideways the whole bone has a 

 slio'ht bend convex backward. The lower half of the shaft 

 becomes subcylindrical as it descends. The ridge, commencing 

 below the lesser sigmoid cavity, is strongly marked and more 

 vertical than in Man. The distal end of the ulna suddenly ex- 

 pands into a convex reniform articular surface, thickest at the 

 middle, where it plays upon the lateral concavity of the radius. 

 The difference from the Chimpanzee, most significant of their 

 relative position in the Quadrumanous series, presented by the 

 antibrachium of the Gorilla, is its inferiority of length compared 

 with the humerus ; fig. 346, with figs. 345 and 180. 



The bones of the wrist, 56, agree in number and relative position 

 with those of Man ; but the differences of shape and proportion 

 give a greater breadth to the carpal segment in proportion to its 

 length, in the Gorilla. The radial surface is nearly circular in 

 shape, instead of being oval and oblong as in Man. The pisi- 

 forme of the Gorilla is much longer in proportion to its breadth 

 than in Man; whilst the articular surface for the cuneilbrme 

 is but little larger: its superior length gives stronger leverage 

 to the great ulnar flexor of the wrist. Tlie trapezium of the 

 Gorilla differs most from its homologue in Man, by the production 

 of its outer unarticular surface into two diverging tuberous pro- 

 cesses : the articular surface, moreover, for the metacarpal of the 

 thumb is relatively much smaller than in Man. This meta- 

 carpal, 57, is a little longer than in Man, but not quite so broad : 

 the proximal trochlea is more concave vertically and more convex 

 transversely, and the distal surface is more convex. The proximal 

 phalanx is one fifth longer, and is more slender than in Man. 

 The metacarpals of the other fingers are more than one third 

 larger and longer than in Man, their shaft is more bent; the 



' It may be noted tliat the hair covering the arm and fore-arm has a direction 

 corresponding with that of the medullary arteries of the bracliial and antibiacliial 

 bones. 



