The head leaves the capsule through the rent made in its lower part, and, either from a continuation of the force or from contraction of the muscles inserted into the inter-tubercular (bicipital) groove, particularly the great pectoral, passes medially under cover of the biceps and coraco-brachialis till it comes to rest against the anterior surface of the neck of the scapula, just below the coracoid process. The anatomical neck of the humerus presses against the anterior edge of the glenoid, and there is frequently an _indentation fracture of the head of the humerus_ where the two bones come into contact (F. M. Caird). The subscapularis is bruised or torn, the muscles inserted into the great tuberosity are greatly stretched, or the tuberosity itself may be avulsed, allowing the long tendon of the biceps to slip laterally, where it may form an impediment to reduction. The axillary (circumflex) nerve is often bruised or torn, and the head of the humerus is liable to press injuriously on the nerves and vessels in the axilla. The _clinical features_ common to all dislocations are prominent, although Dugas' symptom is not constant. [Illustration: FIG. 19.--Sub-coracoid Dislocation of Humerus. (Sir H. J. Stiles' case. Radiogram by Dr. Edmund Price.)] _Treatment._--The guiding principle in the reduction of these dislocations is to make the head of the bone retrace the course it took in leaving the socket. The main obstacles to reduction being muscular contraction and the entanglement of the head with tendons, ligaments, or bony points, appropriate means must be taken to counteract each of these factors. A general anæsthetic is an invaluable aid to reduction, and should be given unless there is some reason for withholding it. It is specially indicated in strong muscular subjects, and in nervous patients who do not bear pain well, and particularly when the dislocation has existed for a day or two. In quite recent cases, however, the surgeon may succeed in replacing the bone by taking advantage of a temporary faintness, or by engaging the patient's attention with other matters while he carries out the appropriate manipulations. When an anæsthetic is employed, the patient should be laid on a mattress on the floor, or on a narrow, firm table; otherwise he should be seated on a chair.