OSTEOLOGY AND ARTHROLOGY 67 



These tuberosities are visible under the skin which covers 

 the superior and lateral parts of the region known as the 

 knee ; but which, we again repeat, is no other than the 

 wrist. 



The ulna has a triangular shaft, situated at the posterior 

 surface of the radius, with which it is fused. It disappears 

 completely at the level of the inferior third of the forearm. 

 Occasionally, in some horses, the ulna is abnormally long, 

 in the form of a slender tongue of bone ; and extends to the 

 neighbourhood of the external tuberosity of the inferior 

 extremity of the radius (see Fig. 79, p. 196). Its superior 

 extremity is chiefly represented by the olecranon process, 

 which is voluminous in bulk, and forms the projection known 

 as the point of the elbow. This process is flattened laterally ; 

 its internal surface is excavated ; the anterior surface, which 

 is concave, forms a part of the great sigmoid cavity ; the 

 remainder of the cavity is formed by the radius. 



In the ass, the ulna is a little longer than in the horse — 

 that is to say, it descends lower ; and the radius is a little 

 more convex anteriorly. 



The carpal bones are seven in number — four in the superior 

 row, and three in the inferior. The trapezium is wanting in 

 the latter. Sometimes, however, in certain varieties of horses 

 the trapezium is developed, but then it is no more than a very 

 small osseous nodule. The pisiform bone, situated at the 

 external part of the first row of bone, is prominent pos- 

 teriorly. It is of rounder form and flattened from without 

 inwards. It articulates with the trapezium and the radius. 

 It presents, on its external surface, a groove for the passage of 

 the tendon of the posterior ulnar muscle, which is named by 

 veterinary anatomists the external flexor of the metacarpus. 



The carpus, as a whole, is of an irregularl}^ cuboid shape ; 

 its anterior surface, slightly convex from side to side, forms 

 the skeleton of the region of the knee (wrist). The meta- 

 carpus is formed of three bones : the principal metacarpal 

 and the two rudimentary ones. 



The principal metacarpal, which forms the region of the 

 canon, is directed vertically ; its anterior surface is slightly 

 convex transversely. This surface is covered by a number 



5-2 



