378 MUSCLES AND FASCIAE. 



The Subscapularis (Fig. 237) is a large triangular muscle, which fills up the 

 subscapular fossa, arising from its internal two-thirds, with the exception of a 

 narrow margin along the posterior border, and the inner side of the superior 

 and inferior angles, which afford attachment to the Serratus Magnus. Some 

 fibres arise from tendinous laminae, which intersect the muscle, and are attached 

 to ridges on the bone ; and others from an aponeurosis, which separates the 

 muscle from the Teres Major and the long head of the Triceps. The fibres 

 pass outwards, and, gradually converging, terminate in a tendon, which is in- 

 serted 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 and 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 

 Latissimus 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. 



POSTERIOR SCAPULAR KEGION. (Fig. 238.) 



Supraspinatus. Teres Minor. 



Infraspinatus. Teres Major. 



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

 humerus, detach the Deltoid and Trapezius from their attachment to the spine of the scapula 

 and acromion process. Remove the clavicle by dividing the ligaments connecting it with the 

 coracoid process, and separate it at its articulation with its scapula ; divide the acromion pro- 

 cess near its root with a saw. The fragments being removed, the tendons of the posterior 

 Scapular muscles 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 supraspinous aponeurosis is a thick and dense membranous layer, which 

 completes the osseo-fibrous case in which the Supraspinatus muscle is con- 

 tained; affording attachment, by its inner surface, to some of the fibres of 

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

 acromial ligament. When this fascia is removed, the Supraspinatus muscle is 

 exposed. 



The Supraspinatus muscle occupies the whole of the supraspinous fossa, 

 arising from its internal two-thirds, and from the strong fascia which covers 

 its surface. The muscular fibres converge to a tendon, which passes across the 

 capsular ligament 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 acro- 

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

 the scapula, the suprascapular vessels and nerve, and upper part of the shoulder- 

 joint. 



The infraspinous aponeurosis is a dense fibrous membrane, covering in the 

 Infraspinatus muscle, and attached to the circumference of the infraspinous 

 fossa. It affords attachment, by its inner surface, to some fibres of that muscle, 

 is continuous externally with the fascia of the arm, and gives off from its under 

 surface intermuscular septa, which separate the Infraspinatus from the Teres 

 Minor, and the latter from the Teres Major. 



