DISSECTING MANUAL. 



nence, being separated from it by a shallow groove (muscu- 

 lo-spiral) which winds round the outer edge. The anterior 

 surface is triangular and has a mesial ridge. The posterior 

 surface is smooth and rounded above, but flattened below. 

 The internal epicond vie is the more prominent ; the external is 

 stunted. [191] 



The lower extremity has two articular surfaces of which the 

 outer (capitellum) , for the radius, is rounded and lies on the an- 

 terior surface and lower border; above this, anteriorly, is a 

 depression (fossa radialis) for the radius. A shallow groove 

 separates the capitellum from the inner articular surface 

 (trochlea), for the ulna. The trochlea is grooved, has promi- 

 nent edges which wind spirally round the lower extremity, 

 curving from behind forward and inward, and its axis slightly 

 oblique to the long axis of the shaft. The inner edge of the 

 trochlea is the sharper and more prominent ; the outer edge is 

 rounded in front, but forms a crest behind the capitellum. 

 Just above the trochlea anteriorly is a depression (coronoid 

 fossa) for the coronoid process of the ulna, and posteriorly there 

 is another (olecranon fossa) for the olecranon; only a thin 

 layer of bone separates these fossa?. [193] 



Ulna. The superior extremity is enlarged and supports the 

 olecranon and coronoid processes. The olecranon process is in 

 line with the shaft ; its triangular posterior surface is smooth ; 

 its superior surface forms, with the posterior, a rectangular 

 projection; the anterior surface helps form the great sigmoid 

 cavity; the anterior border is crescent ic. The coronoid 

 process juts forward from the fore and upper part of the shaft, 

 its upper surface entering into the great sigmoid cavity; the 

 anterior surface is triangular, slopes downward and backward, 

 and ends below in a tubercle ; the inner surface is smooth ; of 

 the lateral margins the inner is the best defined and presents 

 a tubercle where is joins the superior border. The great sig- 

 moid cavity is a semicircular notch, with sharp margins, formed 

 by the olecranon process above and the coronoid below; 



[144] 



