162 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 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 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 olecranpn 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 
Sees? 
