THORACIC LIMBS. • 69 



bone, flattened mediolaterad. It is enlarged at its proximal 

 end and becomes gradually smaller toward the distal end. 



The proximal end is marked ventrally by a deep excava- 

 tion, the semilunar notch, or great sigmoid cavity (//). By 

 the saddle-shap(^d articular surface of the semilunar notch it 

 articulates with the trochlea. This articular surface is divided 

 into two parts by a transverse non-articular area. The distal 

 boundary of the semilunar notch is a blunt process, the coro- 

 noid process (/'), which bears on its lateral surface a concave 

 facet, the radial notch, for the head of the radius. 



The portion of the bone proximad of the semilunar notch is 

 called the olecranon (J). It fits into the olecranon fossa of the 

 humerus when the arm is straightened, and is rough at its end 

 for the insertion of tendons. 



The body of the ulna becomes triangular distad. The 

 distal end is slightly larger than the shaft just proximad of it, 

 and bears on its radioventral side a hemispherical head for 

 articulation with the radius. Distad of the head the bone con- 

 tinues as the flattened styloid process (;;/), which projects distad 

 from its dorsolateral side and is smooth on the medial side of 

 its apex, for articulation with the cuneiform bone of the wrist. 



Carpus (Fig. 51). — The carpus (wrist) consists of seven 

 bones arranged in two rows, three in the proximal row and 

 four in the distal row. Beginning on the medial side of the 

 hand (thumb or radial side), the first bone in the proximal row 

 is the scapholunar (a) (equal to the scaphoid or navicular and 

 lunar of' the human hand). It articulates with the radius. 

 The next is the cuneiform {d), articulating with the styloid 

 process of the ulna, and the next, which is attached to the 

 cuneiform and projects freely ventrad, is the pisiform (r). 



In the distal row the bone on the radial side is the trapezium 

 {d); the next is the trapezoid (r), the next the os magnum (/), 

 and the last the unciform (^). The distal row articulates with 

 the metacarpals or bones of the palm of the hand (i-5). 



In the kitten the scapholunar is represented by three bones, 

 the scaphoid or navicular, on the radial side, the lunare, be- 

 tween the scaphoid and the cuneiform, and a centrale, which 

 lies distad of the other two. 



