232 ACROMIAL REGION. 



pular head of the triceps and integument. By its anterior surface 

 with the subscapularis, latissimus dorsi, coraco-brachialis, short head 

 of the biceps, axillary vessels, and branches of the brachial plexus. By 

 its tipper border it is in relation with the teres minor, from which it 

 is separated by the scapular head of the triceps, and by the lower it 

 forms with the latissimus dorsi the lower and posterior border of the 

 axilla. 



A large triangular space exists between the two teres muscles, 

 which is divided into two minor spaces by the long head of the 

 triceps. 



Actions, The eupra-spinatus raises the arm from the side ; but 

 only feebly, from the disadvantageous direction of the force. The 

 infra-spinatus and teres minor are rotators of the head of the humerus 

 outwards. The most important use of these three muscles is the pro- 

 tection of the joint, and defence against displacement of the head of 

 the humerus, in which action they co-operate with the subscapularis. 

 The teres major combines, with the latissimus dorsi, in rotating the 

 arm inwards, and at the same time carrying it towards the side, and 

 somewhat backwards. 



Acromial Region. 

 Deltoid. 



The convexity of the shoulder is formed by a large triangular 

 muscle, the deltoid (A, delta ; ii$os, resemblance), which arises from the 

 outer third of the clavicle, from the acromion process,and from the whole 

 length of the spine of the scapula. The fibres from this broad origin 

 converge to the middle of the outer side of the humerus, where they 

 are inserted into a rough triangular elevation. This muscle is remark- 

 able for its coarse texture, and for its numerous tendinous intersections 

 from which muscular fibres arise. The deltoid muscle may now be 

 cut away from its origin, and turned down, for the purpose of bring- 

 ing into view the muscles and tendons placed immediately around the 

 shoulder-joint. In so doing, a large bursa will be seen between the 

 under surface of the muscle and the head of the humerus. 



Relations. By its superficial surface with a thin aponeurotic fascia, 

 a few fibres of the platysma myoides, the superficial fascia and in- 

 tegument. By its deep surface with the shoulder-joint, from which 

 it is separated by a thin tendinous fascia, and by a synovial bursa ; 

 with the coraco-acromial ligament, coracoid process, pectoralis minor, 

 coraco-brachialis, both heads of the biceps, tendon of the pectoralis 

 major, tendon of the supra-spimitus, infra-spinatus, teres minor, teres 

 major, scapular and external head of the triceps, the circumflex 

 vessels anterior and posterior, and humerus. By its anterior border 

 with the external border of the pectoralis major, from which it is 

 separated by a cellular interspace, lodging the cephalic vein and 

 descending branch of the thoracico-acromialis artery. Its posterior 



