THE POSTERIOR SCAPULAR REGION. 473 



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 

 outward, 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, the axillary vessels and nerves, and the subscapular vessels 

 and nerves : by its posterior surface, with the scapula and the capsular ligament 

 of the shouldev-joint. Its lower border is contiguous with the Teres major and 

 Latissimus dorsi. 



Nerves. It is supplied by the upper and lower subscapular nerves. 



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

 the arm is raised, it draws the humerus downward. Together with the following 

 muscles it is a defence to the shoulder-joint, as, by their tension, they all prevent 

 displacement of the head of the bone. 



Posterior Scapular Region (Fig. 305). 



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 the scapula : divide the aeromion process 

 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 fascia is a thick and dense membranous layer, which com- 

 pletes the osseo-fibrous case in which the Supraspinatus muscle is contained, 

 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. 

 "W hen 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 sur- 

 face. 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 aeromion, 

 the coraco-acromial ligament, and the Deltoid ; by its under surface, with the 

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



The Infraspinous fascia is a dense fibrous membrane, covering in the Infra- 

 spinatus muscle and attached to the circumference of the infraspinous fossa; it 

 affords attachment, by its inner surface, to some fibres of that muscle. At the point 

 where the Infraspinatus commences to be covered by the Deltoid, this fascia divides 

 into two layers : one layer passes over the Deltoid muscle, helping to form the 

 Deltoid fascia already described ; the other passes beneath the Deltoid to the 

 shoulder-joint. 



The Infraspinatus is a thick, triangular muscle, which occupies the chief part 

 of the infraspinous 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 minor. 

 The fibres converge to a tendon which glides over the external border of the 

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



