206 ACROMIAL REGION DELTOID. 



der, and part of the dorsum of the scapula, the dorsalis scapulae ves- 

 sels, scapular head of the triceps, and shoulder joint. By its upper 

 border with the infra-spinatus ; and by the lower with the latissimus 

 dorsi, teres major, and long head of the triceps. 



The Teres major muscle arises from the lower third of the inferior 

 border of the scapula, encroaching a little upon its dorsal aspect, and 

 is inserted into the posterior bicipital ridge. Its tendon lies imme- 

 diately behind that of the latissimus dorsi, from which it is separated 

 by a synovial membrane. 



Relations. By its posterior surface with the latissimus dorsi, sca- 

 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 upper border it is in relation with 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 



M _ ^ _MWMBHMMM~. *** ^^ %^ * ^ *"" ^M^ ^ ** 



the axilla. 



A large triangular space exists between the twe teres muscles, 

 which is divided into two minor spaces by the long head f tk* 

 triceps. 



Actions. The supra-spinatus raises the arm from the side ; but 

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

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

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

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

 of the ffifmerus, in which action they co-operate with the subscapu- 

 laris. 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; */<>, 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 remarkable for its coarse texture, and the combination-jof 

 tendinous and muscular fibres. 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 integument. By its deep surface with the shoulder joint, from 

 which it is separated by a min tendinous fascia, and by a synovial 

 bursa ; with the coraco-acromial ligament, coracoid process, pecto- 

 ralis minor, coraco-brachialis, both heads of the biceps, tendon of 



