442 MYOLOGY 



tendon of this muscle passes across, and is united with, the posterior part of the 

 capsule of the shoulder-joint. 



Variations. It is sometimes inseparable from the Infraspinatus. 



The Teres major (Fig. 412) is a thick but somewhat flattened muscle, which 

 arises from the oval area on the dorsal surface of the inferior angle of the scapula, 

 and from the fibrous septa interposed between the muscle and the Teres minor 

 and Infraspinatus; the fibers are directed upward and lateralward, and end in a 

 flat tendon, about 5 cm. long, which is inserted into the crest of the lesser tubercle 

 of the humerus. The tendon, at its insertion, lies behind that of the Latissimus 

 dorsi, from which it is separated by a bursa, the two tendons being, however, 

 united along their lower borders for a short distance. 



Nerves. The Supraspinatus and Infraspinatus are supplied by the fifth and sixth cervical 

 nerves through the suprascapular nerve; the Teres minor, by the fifth cervical, through the 

 axillary; and the Teres major, by the fifth and sixth cervical, through the lowest subscapular. 



Actions. The Supraspinatus assists the Deltoideus in raising the arm from the side of the 

 trunk and fixes the head of the humerus in the glenoid cavity. The Infraspinatus and Teres 

 minor rotate the head of the humerus outward; they also assist in carrying the arm backward. 

 One of the most important uses of these three muscles is to protect the shoulder-joint, the Supra- 

 spinatus supporting it above, and the Infraspinatus and Teres minor behind. The Teres major 

 assists the Latissimus dorsi in drawing the previously raised humerus downward and backward, 

 and in rotating it inward; when the arm is fixed it may assist the Pectorales and the. Latissimus 

 dorsi in drawing the trunk forward. 



IV. THE MUSCLES AND FASCLffi OF THE ARM. 



The muscles of the arm are: 



Coracobrachialis. Brachialis. 



Biceps brachii. Triceps brachii. 



Brachial Fascia (fascia brachii; deep fascia of the arm) . The brachial fascia is 

 continuous with that covering the Deltoideus and the Pectoralis major, by means 

 of which it is attached, above, to the clavicle, acromion, and spine of the scapula; 

 it forms a thin, loose, membranous sheath for the muscles of the arm, and sends 

 septa between them; it is composed of fibers disposed in a circular or spiral direc- 

 tion, and connected together by vertical and oblique fibers. It differs in thickness 

 at different parts, being thin over the Biceps brachii, but thicker where it covers 

 the Triceps brachii, and over the epicondyles of the humerus : it is strengthened 

 by fibrous aponeuroses, derived from the Pectoralis major and Latissimus dorsi 

 medially, and from the Deltoideus laterally. On either side it gives off a strong 

 intermuscular septum, which is attached to the corresponding supracondylar 

 ridge and epicondyle of the humerus. The lateral intermuscular septum extends 

 from the lower part of the crest of the greater tubercle, along the lateral supra- 

 condylar ridge, to the lateral epicondyle; it is blended with the tendon of the Del- 

 toideus, gives attachment to the Triceps brachii behind, to the Brachialis, Brachio- 

 radialis, and Extensor carpi radialis longus in front, and is perforated by the radial 

 nerve and profunda branch of the brachial artery. The medial intermuscular 

 septum, thicker than the preceding, extends from the lower part of the crest of 

 the lesser tubercle of the humerus below the Teres major, along the medial supra- 

 condylar ridge to the medial epicondyle; it is blended with the tendon of the 

 Coracobrachialis, and affords attachment to the Triceps brachii behind and the 

 Brachialis in front. It is perforated by the ulnar nerve, the superior ulnar 

 collateral artery, and the posterior branch of the inferior ulnar collateral artery. 

 At the elbow, the deep fascia is attached to the epicondyles of the humerus and 

 the olecranon of the ulna, and is continuous with the deep fascia of the forearm. 



