1 62 Anatomy of the Rabbit. 



joint, or enarthrosis, but the articulating surfaces are somewhat 

 restricted, and the muscular arrangements of the limb are such 

 that the range of lateral motion (abduction and adduction) is small. 

 Immediately in front of the head of the bone there is a small 

 elevation, the medial tuberosity or lesser tubercle (tuberculum 

 minus). It is separated by a longitudinal furrow of the anterior 

 surface, the intertubercular groove (sulcus intertubercularis) , 

 from a much larger lateral elevation, the lateral tuberosity or 

 greater tubercle (tuberculum majus). Extending distad from 

 the latter is a triangular area, the deltoid tuberosity (tuberositas 

 deltoidea) , the tip of which reaches almost to the middle of the bone 

 and forms a pronounced angle on its anterior surface. 



The distal extremity of the humerus bears a grooved articular 

 surface, the trochlea humeri, for articulation with the radius 

 and ulna. On its lateral side is a smaller surface, the capitulum 

 humeri, for articulation with the radius alone. Immediately 

 above the trochlea the medial arid 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 greatly 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.' 



THE RADIUS AND ULNA. 



The radius (Fig. 68) 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 is crossed on 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 



