112 PRACTICAL ANATOMY. 



lodges the long tendon of the biceps muscle ; it is called 

 the bicipital groove. The greater tuberosity presents 

 three facets, to which are attached the supra-spinous, 

 infra-spinous, and teres minor muscles, external rota- 

 tors. To the lesser tuberosity is attached the subscapu- 

 laris, an internal rotator muscle. Just below the tuber- 

 osities the bone presents a constriction, called the surgical 

 neck, on account of the frequency of fracture at this 

 place. 



The shaft is cylindrical above, becomes prismoid 

 below. It presents on its outer surface, about the middle, 

 a shallow groove, which winds spirally from behind down- 

 ward and forward ; it lodges the musculo-spiral nerve and 

 superior profunda artery, and is called the musculo-spiral 

 groove. On the outer surface, at about the middle, is 

 the deltoid surface, for the attachment of the deltoid 

 muscle. The lower half of the shaft is very much flat- 

 tened from before backward, presents three borders ex- 

 ternal, internal, and anterior and three surfaces. The 

 external border begins below the deltoid surface, and 

 terminates at the external epicondyle; it is blunt and 

 rounded above and sharp below. The internal border 

 begins at the middle of the bone, below a roughened 

 surface, which serves for the attachment of the coraco- 

 brachialis muscle ; it runs downward, becomes sharp and 

 crest-like, and terminates at the internal epicondyle, a 

 prominent triangular projection of bone, which affords 

 attachment to the flexor muscles of the forearm. The 

 anterior border is slightly marked, and passes downward 

 from the deltoid surface toward the coronoid depression. 

 The external surface is between the anterior and external 

 borders; it is somewhat rough, for the attachment of the 

 brachialis anticus. The internal surface, smaller than 

 the external, lies between the anterior and internal bord- 



