_Varieties._--Several varieties of dislocation are recognised, according to the position in which the head of the humerus finally rests (Fig. 17). The simplest of these is the _sub-glenoid_ variety, in which the head rests on the long tendon of the triceps, where it arises from the axillary border of the scapula just below the glenoid cavity. In almost all dislocations of the shoulder the head of the bone is at least momentarily in this position, but the sharp edge of the scapula and the rounded head are ill adapted to one another, and the position is not long maintained. The subsequent course taken by the humerus depends upon the nature and direction of the force, the position of the limb at the moment of injury, and the relative strength and capacity for effective action of the different groups of muscles acting upon the bone. [Illustration: FIG. 17.--Diagram of most common varieties of Dislocation of the Shoulder.] In the great majority of cases it passes forward and medially, and comes to lie against the anterior surface of the neck of the scapula, under cover of the tendons of origin of the biceps and coraco-brachialis muscles, constituting the _sub-coracoid dislocation_. Much less frequently it passes under cover of the pectoralis minor and against the edge of the clavicle--the _sub-clavicular_ variety. In rare cases the head passes backward and lies against the spine on the dorsum of the scapula, beneath the infra-spinatus muscle--the _sub-spinous_ variety. Other varieties are so rare that they do not call for mention.