POSTERIOR SCAPULAR REGION. 227 



a broad and thick tendon, which is inserted into the lesser tuberosity of the 

 humerus. The substance of the muscle is traversed by several intersecting 

 membranous layers from which muscular fibres arise, the intersections 

 being attached to the ridges on the surface of the scapula. Its tendon 

 forms part of the capsule of the joint, glides over a large bursa which 

 separates it from the base of the coracoid process, and is lined by a pro- 

 longation of the synovial membrane of the articulation. 



Relations. By its anterior surface with the serratus magnus, coraco- 

 brachialis, and axillary vessels and nerves. By its posterior surface with 

 the scapula, the subscapular vessels and nerves, and the shoulder joint. 



JJction. It rotates the head of the humerus inwards, and is a powerful 

 defence to the joinj. When the arm is raised, it draws the humerus 

 downwards. 



Posterior Scapular Region. 



Supra-spinatus, Teres minor, 



Infra-s'pinatus, Teres major. 



The SUPRA-SPINATUS muscle (supra, above ; spina, the spine) arises 

 from the whole of the supra-spinous fossa, and is inserted into the upper- 

 most depression on the great tuberosity of the humerus. The tendon of 

 this muscle cannot be well seen until the acromion process is removed. 



Relations. By its upper surface, with the trapezius, the clavicle, acro- 

 mion, and coraco-acromion ligament. From the trapezius it is separated 

 by a strong fascia. By its lower surface, with the supra-spinous fossa, the 

 supi a-scapular vessels and nerve, and the upper part of the shoulder joint, 

 forming part of the capsular ligament. 



The INFRA-SPINATUS (infra, beneath ; spina, the spine) is covered in by 

 a layer of tendinous fascia, which must be removed before the fibres of the 

 muscle can be seen, the deltoid muscle having been previously turned 

 down from its scapular origin. It arises from the whole of the infra-spinous 

 fossa, and from the fascia above-mentioned, and is inserted into the middle 

 depression upon the greater tuberosity of the humerus. 



Relations. By its posterior surface, with the deltoid, latissimus dorsi 

 and integument. By its anterior surface, with the infra-spinous fossa, su- 

 perior and dorsal scapular vessels, and shoulder joint ; its tendon being 

 lined by a prolongation from the synovial membrane. By its upper border, 

 it is in relation with the spine of the scapula, and by the lower, with the 

 teres minor, with which it is closely united. 



The TERES MINOR muscle (teres, round) arises from the middle third 

 of the inferior border of the scapula, and is inserted into the lower depres- 

 sion on the great tuberosity of the humerus. The tendons of these three 

 muscles, with that of the subscapularis, are in immediate contact with the 

 shoulder joint, and form part of its ligamentous capsule, thereby preserving 

 the solidity of the articulation. They are therefore the structures most 

 frequently ruptured in dislocation of the head of the humerus. 



Relations. By its posterior surface, with the deltoid, latissimus dorsi 

 and integument. By its anterior surface, with the inferior border, and 

 part of the dorsum of the scapula, the dorsalis scapulae vessels, 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. 



