384 THE MUSCLES AND FASCIA. 



the lower two-thirds of the groove on the axillary border of the bone. 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 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 anterior part 

 of 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. Its anterior surface forms a considerable part of the posterior wall 

 of the axilla, and is in relation with the Serratus magnus, Coraco-brachialis, and 

 Biceps, the axillary vessels and brachial plexus of nerves, and the subscapular 

 vessels and nerves. By its posterior surface, with the scapula 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 fifth and sixth cervical nerves through 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 forward and downward. It is a powerful 

 defence to the front of the shoulder-joint, preventing displacement of the head of 

 the bone. 



5. Posterior Scapular Region (Fig. 232). 



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 acromion 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. 

 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 sur- 

 face. The muscular fibres converge to a tendon which passes across the upper 

 part of 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 acromion, 

 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-j oint. 



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 



