128 SURGICAL ANATOMY OF 



The great power of all these muscles upon this joint, 

 which owes its great extent of motion to the shallow 

 glenoid cavity and large head of humerus, and the 

 laxity of its capsule, favors dislocation under certain cir- 

 cumstances ; and were it not for the bony arch formed 

 by the coracoid and acromion processes, and the liga- 

 ment between them, the long head of the biceps passing 

 through the capsule over the head of the bone and blend- 

 ing with the glenoid ligament, and the mobility of the 

 scapula, such accidents would be still more frequent. 



The anatomical position of the head of the humerus 

 with regard to the neighboring bony structures after its 

 dislocation may be generalized thus, subglenoid, sub- 

 clavicular ', subcoracoid, subspinous. 



In the condition termed subglenoid, the head of the 

 humerus rests on the inferior border of the scapula, 

 below the glenoid cavity, between the subscapularis and 

 long head of triceps ; and the peculiar numbness in the 

 hand and arm, and frequent coldness and oedema in the 

 limb, are due to pressure upon the brachial plexus and 

 axillary vessels. In the subclavicular variety, the head 

 of the bone lies below the clavicle, internal to the cora- 

 coid process, upon the second and third ribs, and be- 

 neath the pectoral muscles. In the subcoracoid, the 

 head of the bone lies deeply in the upper and inner part 

 of the axilla, below the coraco-brachialis and pectoralis 

 muscles. In the subspinous form, the head of the bone 

 lies behind the glenoid cavity, below the spine, and be- 

 tween the infra-spinatus and teres minor muscles. These 

 may be regarded as the complete forms, which are, of 

 course, liable to modifications. 



That portion of the bone belonging to the region of 

 the shoulder that is to say, as low down as the inser- 



