288 SKELETON OF THE EABBIT 



suprartroehlear foramen : the posterior or 

 olecranon fossa is much the larger of the two, 

 and lodges the olecranon process of the ulna 

 when the arm is extended, 



2. The fore-arm contains two bones, of about equal size, 



immovably articulated, though not ankylosed, with 

 each other. 



i. The radius, or preaxial bone, lies in front of 

 the ulna at the proximal end of the forearm, 

 but in the distal half lies along its inner or 

 preaxial side. 



It is an elongated bone, slightly curved 

 forwards. Its proximal end or head articulates 

 with both grooves of the trochlea of the 

 humerus, and also with the anterior surface 

 of the ulna : its distal and larger end articu- 

 lates with the bones of the wrist. 



ii. The ulna, or postaxial bone of the forearm, has 

 a greatly enlarged proximal end, on the 

 anterior surface of which is the sigmoid notch, 

 for articulation with the trochlea, and also 

 two small articular surfaces for the radius. 

 Behind the elbow-joint, the bone forms the 

 large, laterally compressed olecranon process. 

 The distal end of the ulna is small and articu- 

 lates with the carpus. 



3. The wrist. In the rabbit the wrist or carpus consists 



of nine small bones, of which one, the pisiform, is of 

 a different nature from the others, being merely a 

 sesamoid bone or ossification in the tendon of a 

 muscle. The arrangement of the remaining eight 

 can only be understood by comparison with more 

 primitive types. 



The typical carpus consists of nine bones, arranged 

 in a proximal row of three, articulating with the 

 radius and ulna ; a distal row of five, each of which 

 supports one of the digits ; and a central bone wedged 



