The Region of the Shoulder. 23 



the upper facet of the greater tuberosity, besides assisting 

 in preventing displacement of the humerus upwards, acts, 

 witlh the deltoid, in raising the arm from the side. 2. The 

 infra-spinatus, from the inner two-thirds of the infraspi- 

 nous fossa, and inserted into the middle facet of the greater 

 tuberosity, protects the joint, behind, and rotates the head 

 of the bone, outwards. 3. The teres minor from the up- 

 per two-thirds of the posterior surface of axillary border 

 of the scapula ; into the lowest facet of the tuberosity, has 

 the same action as the imfra-spinatus. 4. The triceps by 

 three heads one, from the triangular depression below 

 the glenoid cavity ; a second, from the posterior surface of 

 the shaft of the humerus above the musculo-spiral groove, 

 and a third, from the same surface below the groove ; into 

 two fibrous lamellae one, occupying the posterior surface 

 and the otiher, the substance of the muscle which lamel- 

 lae, uniting, are inserted into the back part of the upper 

 surface of the olecranon. This muscle protects the lower 

 part of the shoulder joint, preventing displacement down- 

 wards and backwards, and extends the forearm, while its 

 long head assists the latissimus dorsi and teres major in 

 drawing the humerus backwards. 5. The deltoid from 

 the outer third of the anterior surface of the clavicle, from 

 tihe outer margin of acromion and the lower lip of the pos- 

 terior border of the spine of the scapula ; into the middle 

 of the outer surface of the shaft of the humerus, raises the 

 arm to a right angle with the body, its anterior fibres as- 

 sisting the pectoralis major in drawing the arm forwards, 

 while its posterior, with the teres major and the latissimus 

 dorsi, draw it backwards. 6. The coraco-brachialis, from 

 the apex of the coracoid process in common with the short 

 head of the biceps ; into the middle of the inner surface of 

 the shaft of the humerus, assists in elevating the arm, at 

 the same time drawing it inwards and forwards. 7. The 



