THE SHOULDER REGION 15 



immediately above the shoulder-joint and is partly inserted into the capsule. 

 It initiates the movement of abduction and assists the deltoid. 



The Infra-spinatus arises from the infra-spinous fossa, and is inserted 

 into the postero-superior surface of the greater tubercle. It passes over the 

 posterior surface of the shoulder-joint and partially blends with the capsule ; 

 it is the chief lateral rotator of the humerus. 



Both these muscles are supplied by the supra-scapular nerve (C. 5 and 6), 

 which passes through the scapular notch below the ligament. (The results 

 of injury to this nerve are described on p. 98.) 



The Teres minor lies in relation to the posterior aspect of the capsule 

 of the shoulder-joint, and its action is the same as that of the infra-spinatus. 

 It is supplied by the axillary (circumflex) nerve (C. 5 and 6). 



Ossification of the Proximal Extremity of the Humerus. 



At birth the proximal extremity of the humerus is entirely 

 cartilaginous. During the first year a secondary centre appears 

 for the articular head of the bone ; at the second year, one 

 appears for the greater tubercle ; at the end of the third year, 

 one appears for the lesser tubercle. These three centres unite 

 to form the proximal epipbysis of the humerus during the 

 seventh year. It fits like a cap over the proximal end of the 

 diaphysis, which is somewhat pointed (Fig. 5), and it fuses 

 with the diaphysis between eighteen and twenty-five. The 

 epiphyseal line passes distal to the tubercles, but on the medial 

 side it coincides with the margin of the articular head of the bone. 



Ossification of glenoid cavity (p. 13). 



The Shoulder-Joint. The articular surface of the glenoid 

 cavity is slightly concave and is small in comparison with the 

 head of the humerus, which forms a large convex surface, 

 directed upwards, medially, and slightly backwards. The 

 glenoid cavity is enlarged and deepened by the labrum glenoidale 

 (glenoid ligament), which is attached to its margins. 



The Capsule, which is very large and remarkably loose, 

 obtains a wide range of movement for the joint. Proximally, 

 it is attached to the labrum glenoidale, and above, to the bone 

 immediately beyond the origin of the long head of the biceps. 

 On the humerus it is attached to the anatomical neck, laterally, 

 but to the surgical neck, on the medial side. The line of 

 attachment of the capsule crosses the epiphyseal line, so that 

 the lateral portion of the epiphysis (the tuber osities) is extra-capsutar , 

 while the medial part of the proximal end of the diaphysis is 

 intra-capsular. 



The capsule is strengthened anteriorly by the three gleno- 

 humeral ligaments, and above by the coraco-humeral ligament. 

 These accessory bands blend with the capsule so closely that 



