THE UPPER EXTREMITIES. 175 



broken and occasionally the neck is fractured. Tumors 

 occur and may necessitate the amputation of the whole 

 upper extremity. 



The Humerus. The bone of the upper arm, the hu- 

 merus, is the largest bone in the upper extremity and 

 articulates with the scapula above and with the ulna 

 and radius below. At its upper end are the head and 

 the anatomical neck, with the greater tuber osity external 

 to and the lesser tuberosity in front of them. The con- 

 striction of the surgical neck is below the tuberosities, 

 and extending from between them downward and in- 

 ward along the upper third of the bone is the bicipital 

 groove for the long head of the biceps. Though round 

 above, below the shaft becomes flattened from before 

 backward and curves slightly forward, terminating in 

 the internal and external condyles, from the former of 

 which the flexors and the round pronator arise and 

 from the latter the extensors and supinators. From 

 the external condyle also there projects in front the ra- 

 dial head or capitellum for articulation with the radius. 

 Internally to the capitellum in front and in a corre- 

 sponding position on the back of the bone are the troch- 

 lear surfaces for articulation with the ulna, there be- 

 ing a depression in front called the coronoid fossa for the 

 reception of the coronoid process of the ulna in flexion 

 of the forearm, and another depression behind, the 

 olecranon fossa, to receive the tip of the olecranon 

 process during extension. On the lower half of the 

 humerus at the back is the spiral groove for the musculo- 

 spiral nerve and the superior profunda artery, while the 

 ulnar nerve runs in a groove back of the internal condyle. 



The humerus is almost completely covered with mus- 

 cles, the only part that is subcutaneous being a small 

 portion of the external and internal condyles. The 

 head can be felt under the muscles and the greater 

 tuberosity forms the point of the shoulder. When the 

 arm is at the side, the biceps appears at the front and 

 inner side and the brachialis anticus on either side be- 



