ULNA. 71 



the lateral ligament; the external, which is prominent and called 

 tlie external tuberosity, giving origin to the extensor pedis and 

 extensor suffraginis muscles. Posteriorly, two concave facets 

 articulate with the ulna. 



The distal extremity, like the proximal, is widest from side to 

 side ; its articular surface is divided into three facets, the internal 

 of which, the largest, and quadrilateral in shape, articulates with 

 the scaphoid bone ; the middle, resembling the internal, but 

 smaller, articulates with the lunar bone ; and the external, the 

 smallest, oval in shape and convex, articulates with the cuneiform 

 bone and the trapezium. The whole articular surface is sur- 

 rounded by a prominent ridge for the capsular ligament. The 

 anterior part of this extremity is irregular, and has two deep 

 vertical grooves for the tendons of the extensor muscles, and 

 a shallow, oblique one, in which the tendon of the extensor 

 metacarpi obliquus muscle plays. Laterally, two prominent 

 processes, the internal being the largest, give attachment to the 

 lateral ligaments ; the external of these processes is grooved for 

 the passage of the extensor suffraginis tendon. 



ULNA. 

 (Pl. L L'.) 



The ulna is an irregular bone, in form triangular, with the base 

 uppermost, and is placed on the supero-posterior part of the 

 radius. This bone, which grows but little after birth, is larger 

 in the young animal, proportionately to its ultimate size, than 

 any other bone. It possesses a body and two extremities. 



The body is triangular, and has three surfaces and three 

 borders. The anterior surface is the counterpart of the posterior 

 surface of the radius a.gainst which it is applied, having superiorly 

 two convex facets to articulate with the concave ones on the head 

 of the radius ; below these is a rough portion for the attachment 

 of the interosseous ligaments, and still lower, a shallow transverse 

 groove which assists in the formation of the radio-ulnar arch, 

 inferior to which is a roughened surface for the attachment of the 

 ligaments, in which ossification takes place in the adult animal. 

 The external surface is flattened and covered by the flexor 

 metacarpi externus muscle, and. the excavated internal face 

 gives attachment to the ulnaris accessorius, and is covered by 

 the flexor pedis muscles. The lateral borders are thin, and have 



