THE HUMERUS. 



251 



nal condyles. The articular surface extends a 

 little lower than the condvles. and is curved 

 slightly forward, so as to occupy the more ante- 

 rior part of the bone ; its greatest breadth is in 

 the transverse diameter, and it is obliquely di- 

 rected, so that its inner extremity occupies a 

 lower level than the outer. The outer portion of 

 the articular surface presents a smooth, rounded 

 eminence, which has received the name of the 

 capitfUuin. or /v/</V'// h'.-'nl of the humerus ; it 

 articulates with the cup-shaped depression on 

 the head of the radius, and is limited to the 

 front and lower part of the bone, not extending 

 as far back as the other portion of the articular 

 surface. On the inner side of this eminence is 

 a shallow groove, in which is received the inner 

 margin of the head of the radius. Above the 

 front part of the capitellum is seen a slight de- 

 pression which receives the anterior border of the 

 head of the radius when the forearm is flexed. 

 The inner portion of the articular surface, the 

 trochlea, presents a deep depression between 

 two well-marked borders. This surface is con- 

 vex from before backward, concave from side to 

 side, and occupies the anterior, lower, and pos- 

 terior parts of the bone. The external border, 

 less prominent than the internal, corresponds to 

 the interval between the radius and the ulna. 

 The internal border is thicker, more prominent, 

 and consequently of greater length, than the 

 external. The grooved portion of the articular 

 surface fits accurately within the greater sigmoid 

 cavity of the ulna : it is broader and deeper on 

 the posterior than on the anterior aspect of the 

 bone, and is inclined obliquely from behind for- 

 ward and from without inward. Above the front 

 part of the trochlear surface is seen a smaller 

 depression, the coronoid fossa, which receives the 

 coronoid process of the ulna during flexion of the 

 forearm. Above the back part of the trochlear 

 surface is a deep, triangular depression, the olec- 

 i'finon fossa, in which is received the summit of 

 the olecranon process in extension of the forearm. 

 These fossa? are separated from one another by a 

 thin, transparent lamina of bone, which is some- 

 times perforated, forming the supratrochlear for- 

 aiion : their upper margins afford attachment to 

 the anterior and posterior ligaments of the elbow- 

 joint, and they are lined, in the recent state, by 

 the synovial membrane of this articulation. The 

 articular surfaces, in the recent state, are covered 

 with a thin layer of cartilage. The external con- 

 dyle is a small, tubercular eminence, less promi- 

 nent than the internal, curved a little forward, 

 and giving attachment to the external lateral lig- 

 ament of the elbow-joint, and to a tendon common 

 to the origin of some of the extensor and supi- 



f 7 



J rocnt 



FIG. 198- Left humerus. Posterior surface. 



