202 ANATOMY OF THE RABBIT 



humeri, for articulation with the radius alone. Immediately above 

 the trochlea the medial and lateral portions of the bone are 

 thickened to form two areas for muscular attachment. One of 

 these, the lateral epicondyle (epicondylus lateralis), is a general 

 point of origin for the extensor muscles of the dorsal surface of 

 the hand, while the other, the medial epicondyle (epicondylus 

 medialis), is a similar point of origin for the flexor muscles of the 

 ventral or volar surface. Between the epicondyles the extremity 

 of the bone is greatly excavated, so that the projecting portions 

 of the radius in front and of the ulna behind are received into 

 depressions of the surface when the forearm is respectively flexed 

 or extended. On the anterior side is the radial fossa (fossa 

 radialis); on the posterior side the olecranon fossa (fossa olecrani), 

 so-called because it accommodates the olecranon process of the 

 ulna. 



Between the radial and olecranon fossae the bone is reduced to 

 a very thin lamina, which is sometimes pierced by an opening of 

 very variable size, the supratrochlear foramen.^ 



The Radius and Ulna 



The radius (Fig. 94) is the shorter of the two bones of the 

 forearm, since its proximal extremity does not extend backward 

 beyond the front of the elbow-joint. It is anterodorsal in its general 

 position, but crosses the ulna in such a way that its proximal 

 extremity tends to be lateral, while its distal extremity is medial. 

 The proximal extremity, termed the head of the radius (capitulum 

 radii) is immovably articulated with the ulna. It bears an ex- 

 tensive articular surface, meeting both trochlea and capitulum of 

 the humerus, and thus forming a considerable portion of the elbow- 

 joint. The body of the. bone is solidly united with the ulna by 

 the interosseous ligament of the forearm. The distal extremity 

 is largely formed by an epiphysis, which is well marked even in 

 older animals. It bears a grooved, carpal articular surface (facies 

 articularis carpea), for articulation with the navicular and lunate 

 bones. 



The ulna (Fig. 94) is a somewhat S-shaped bone, the shaft of 

 which is vertically flattened, so that it possesses two main surfaces, 



'In an examination of 255 specimens, this was found in 173, or 68 per cent. 



