ANATOMY AND PHYSIOLOGY 



The clavicula is easily broken, especially in children, being fre- 

 quently the seat of "green-stick" fracture. (See p. 77.) 



The clavicula and scapula together form the 

 shoulder-girdle, which is open at the back, 

 but closed in front by the sternum placed be- 

 tween the two claviculae. 



THE ARM OR BRACHIUM 



Humerus.' Long in structure and shape, 

 having a shaft with a medullary canal and two ex- 

 tremities. 



The upper extremity (proximal extremity) 

 includes the head, neck and tubercles. 



The head articulates with the glenoid cavity 

 of the scapula to form the shoulder- joint; the 

 short, thick, anatomic neck joins the head to the 

 shaft, and just below the neck are the greater and 

 lesser tubercles for the attachment of muscles to 

 abduct and rotate the arm. The lower extremity 



FIG. 51. LEFT CU rves slightly forward and presents two pro- 

 HUMERUS, ANTE- . -.., 



RIOR ASPECT. jections at the sides called the medial and lateral 



i, Shaft or body; epicondyles; the medial is the longer and conse- 



2, head; 3, anatomic , . . 



neck; 4, greater tu- quently it is more frequently broken oft. Be- 

 berdej o', ^T",^ tween t ^ ie epicondyles are the articular surfaces 

 markings for mus- for the elbow-joint, the trochlea for the ulna and 



cles; 10, orifice for , . . . , .. 



nutrient artery; n, the capitulum for the radius. 



capitulum; 12 tro- The sha f t has three borders and three sur- 



chlea; 13, 14, lateral 



and medial epicon- faces like that of all long bones (on the fibula 

 anTmedial borders; a fourth border and surface are described). 



The Anterior and medial borders run from the greater 

 and lesser tubercles. In the upper part they are called 

 the crests of the tubercles and the groove for the long tendon of the biceps 

 muscle is between them (formerly called bicipital groove as the borders were 

 called bicipital ridges). 



The broad, shallow groove containing the radial nerve winds 

 across the posterior surface. 



Note. The slender portion of the shaft just below the tubercles 

 is called the surgical neck, because it is so often fractured. 



