300 MUSCLES AND FASCI.E. 



the long licad of the Triceps. The fibres pass outwards, and, gradually converging, 

 terminate in a tendon, which is inserted into the lesser tuberosity of the humerus. 

 Those fibres which arise from the axillary border of the scapula are inserted into 

 the neck of the humerus to the extent of an inch below the tuberosity. The tendon 

 of the muscle is in close contact with the capsular ligament of the shoulder-joint, 

 and glides over a large bursa, which separates it from the base of the coracoid 

 process. This bursa communicates with the cavity of the joint by an aperture in 

 the capsular ligament. 



Relations. By its anterior surface, with the Serratus magnus, Coraco-brachialis, 

 and Biceps, and the axillary vessels aud nerves. By its posterior surface, with 

 the scapula, the subscapular vessels and nerves, and the capsular ligament of the 

 shoulder-joint. Its lower border is contiguous with the Teres major and Latissi- 

 mus dorsi. 



Nerves. It is supplied by the subscapular nerves. 



Actions. The Subscapularis rotates the head of the humerus inwards ; when 

 the arm is raised, it draws the humerus downwards. It is a powerful defence to 

 the front of the shoulder-joint, preventing displacement of the head of the bone 

 forwards. 



POSTERIOE SCAPULAE EEGION. 



i 



Supra-spinatus. Teres Minor. 



Infra-spinatus. Teres Major. 



Dissection. To expose these muscles, and to examine their mode of insertion into the hume- 

 rus, detach the Deltoid and Trapezius from their attachment to the spine of the scapula and acro- 

 mion process. Remove the clavicle by dividing the ligaments connecting it with the coracoid 

 process, and separate it at its articulation with the scapula : divide the acromion process near its 

 root with a saw, and, the fragments being removed, the tendons of the posterior Scapular mus- 

 cles will be fully exposed, and can be examined. A block should be placed beneath the shoulder- 

 joint, so as to make the muscles tense. 



The supra-spinous aponeurosis is a thick and dense membranous layer, which 

 completes the osteo-fibrous case in which the Supra-spinatus muscle is contained ; 

 affording attachment, by its inner surface, to some of the fibres of this muscle. 

 It is thick internally, but thinner externally under the coraco-acromial ligament. 

 When this fascia is removed, the Supra-spinatus muscle is exposed. 



The Supra-spinatus muscle occupies the whole of the supra-spinous fossa, arising 

 from its internal two-thirds, and from a strong fascia which covers its surface. 

 The muscular fibres converge to a tendon, which passes across the capsular liga- 

 ment of the shoulder-joint, to which it is intimately adherent, and is inserted into 

 the highest of the three facets on the great tuberosity of the humerus. 



Relations. By its upper surface, with the Trapezius, the clavicle, the acromion, 

 the coraco-acromial ligament, and the Deltoid. By its under surface, with the 

 scapula, the supra-scapular vessels and nerve, and upper part of the shoulder- 

 joint. 



The infra-spinous aponeurosis is a dense fibrous membrane, covering in the 

 Infra-spinatus muscle, and attached to the circumference of the infra-spinous fossa ; 

 it affords attachment, by its inner surface, to some fibres of this muscle, is con- 

 tinuous externally with the fascia of the arm, and gives off from its under surface 

 intermuscular septa, which separate the Infra-spinatus from the Teres minor, and 

 the latter from the Teres major. 



The Infra-spinatus is a thick triangular muscle, which occupies the chief part 

 of the infra-spinous fossa, arising by fleshy fibres, from its internal two-thirds ; 

 and by tendinous fibres, from the ridges on its surface : it also arises from a strong 

 fascia which covers it externally, and separates it from the Teres major and Teres 

 minor. The fibres converge to a tendon, which glides over the concave border of 

 the spine of the scapula, and, passing across the capsular ligament of the shoulder- 

 joint, is inserted into the middle facet on the great tuberosity of the humerus. 



