316 .THE SKELETON OF THE EABBIT. 



tuberosity, a large roughened projection con- 

 tinued as a ridge down the anterior surface of 

 the bone as far as its middle. 



The trochlea at the distal end of the bone 

 is an oblique pulley-like surface, divided in 

 front by a ridge, and articulating with the 

 radius and ulna to form the elbow-joint. 

 Immediately above the trochlea, in front and 

 behind, are the supra-trochlear fossae, which 

 communicate with each other through the 

 supra-trochlear 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 forearm 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 convex 

 forwards. Its proximal end or head articu- 

 lates 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 an- 

 terior surface of which are 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. 



