THE SKELETAL SYSTEM 41 



The radius in the adult horse is united to the ulna to form what 

 appears to be one bone, but in the fetus and young animal there 

 are two distinct bones. The radius is much larger than the ulna. 

 It is a long bone situated between the humerus and the carpus in a 

 nearly vertical direction, and presents for description a shaft and 

 two extremities. The shaft is curved convexly forward, and 

 presents two surfaces and two borders. The anterior surface is 

 convex and smooth, while the posterior surface is concave in its 

 length and flattened transversely. On the external part of the 

 posterior surface there is a rough area for the attachment of the 

 ulna. The borders are rounded, the inner one is not covered by 

 muscles. The upper extremity carries two shallow cavities for 

 articulation with the distal end of the humerus, the inner of which 

 is the larger. Posteriorly are two facets for articulation with the 

 ulna. In front at the inner side is the large bicipital tuberosity, 

 to which the lower tendon of the biceps muscle is inserted. The 

 distal extremity is composed of three facets for articulation with 

 the proximal row of carpal bones. 



The ulna is a remarkably small bone occupying a position 

 behind the radius and distal part of the humerus. It presents a 

 shaft and two extremities. The shaft is three sided and tapers 

 toward the lower extremity. The anterior surface is attached to 

 the rough area noticeable on the corresponding part of the radius. 

 The internal surface is concave and smooth, while the outer is 

 flattened. The proximal extremity forms the bulk of the bone 

 and projects upward and backward. Its summit is termed the 

 olecranon process and corresponds to the "point of the elbow" 

 in man. The anterior border bears the semilunar notch. 



The bones of the carpus are either seven or eight in number and 

 arranged in two rows. Named from within outward the upper 

 row is composed of the radial, intermediate, ulnar, and accessory 

 carpal bones; the lower row is made up by the first, second, third, 

 and fourth carpal bones. The first carpal is often absent or the 

 size of a pea. The accessory and the first carpals are not in the 

 line of weight. The carpus, as a whole, has four surfaces. The 

 anterior surface is convex and hes further back than the distal 

 end of the radius, thus affording protection to the joint when the 

 animal falls. The posterior surface is very rough in the macerated 

 state, but is leveled by the thick posterior ligament in the hving 



