ULNA. 71 



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

 the 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 conve:i, articulates with the cuneiform bone 

 and the trapezium. > The whole articular surface is surrounded 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. I. L'.) 



The ulna is an irregular bone, in form triaiigular, 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 hody is triangular, and has three surfaces and three 

 borders. The anterior surface is the counterpart of the posterior 

 surface of the radius against which it is applied, having superiorly 

 tvv^o convex facets to articulate with the concave ones 0:^1 the head 

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

 of the interosseous lio-aments, and still lower, a shallow transverse 

 groove v/hich assists in the formation of the radio-ulnar arch, 

 inferior to which is a roughened curface 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 inteimal face 

 gives attachment to the ulnaris accessorius, and is covered by 

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



