386 THE MUSCLES AND FASCIA. 



The Teres major is a thick but somewhat flattened muscle, which arises from the 

 oval surface on the dorsal aspect of the inferior angle of the scapula, and from the 

 fibrous septa interposed between it and the Teres minor and Infraspinatus ; the 

 fibres are directed upward and outward, and terminate in a flat tendon, about two 

 inches in length, which is inserted into the inner bicipital ridge of the humerus. 

 The tendon of this muscle, at its insertion into the humerus, lies behind that of the 

 Latissimus dorsi, from which it is separated by a synovial bursa, the two tendons 

 being, however, united along their lower borders for a short distance. 



Relations. By its posterior surface, with the Latissimns dorsi below, and the 

 long head of the Triceps above. By its anterior surface, with the Subscapularis, 

 Latissimus dorsi, Coraco-brachialis, short head of the Biceps, the axillary vessels, 

 and brachial plexus of nerves. Its upper border is at first in relation with the 

 Teres minor, from which it is afterward separated by the long head of the Triceps. 

 Its lower border forms, in conjunction with the Latissimus dorsi, part of the 

 posterior boundary of the axilla. The Latissimus dorsi at first covers the origin 

 of the Teres major, then wraps itself obliquely round its lower border, so that its 

 tendon ultimately comes to lie in front of that of the Teres major. 



Nerves. The Supra- and Infra-spinatus muscles are supplied by the fifth and 

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

 fifth cervical, through the circumflex; and the Teres major, by the fifth and sixth 

 cervical, through the lower subscapular. 



Actions. The Supraspinatus assists the Deltoid in raising the arm from the 

 side, and fixes the head of the humerus in the glenoid cavity. The Infraspinatus 

 and Teres minor rotate the head of the humerus outward : when the arm is raised, 

 they assist in retaining it in that position and carrying if backward. One of the 

 most important uses of these three muscles is the great protection they afford to 

 the shoulder-joint, the Supraspinatus supporting it above, and preventing displace- 

 ment of the head of the humerus upward, while the Infraspinatus and Teres minor 

 protect it behind, and prevent dislocation backward. The Teres major assists the 

 Latissimus dorsi in drawing the humerus downward and backward, when pre- 

 viously raised, and rotating it inward; when the arm is fixed, it may assist the 

 Pectoral and Latissimus dorsi muscles in drawing the trunk forward. 



THE ARM. 



6. Anterior Humeral Region (Fig. 230). 



Coraco-brachialis. Biceps. Brachialis anticus. 



Dissection. The arm being placed on the table, with the front surface uppermost, make 

 a vertical incision through the integument along the middle line, from the outer extremity of 

 the anterior fold of the axilla to about two inches below the elbow-joint, where it should be 

 joined by a transverse incision, extending from the inner to the outer side of the forearm ; the 

 two flaps being reflected on either side, the fascia should be examined (Fig. 22S). 



The deep fascia of the arm is continuous with that covering the Deltoid and 

 the great Pectoral muscles, by means of which it is attached, above, to the 

 clavicle, acromion, and spine of the scapula ; it forms a thin, loose, membranous 

 sheath investing the muscles of the arm, sending down septa between them, and 

 composed of fibres disposed in a circular or spiral direction, and connected together 

 by vertical and oblique fibres. It differs in thickness at different parts, being thin 

 over the Biceps, but thicker where it covers the Triceps, and over the condyles of 

 the humerus ; it is strengthened by fibrous aponeuroses, derived from the Pectoralis 

 major and Latissimus dorsi on the inner side, and from the Deltoid externally. 

 On either side it gives off a strong intermuscular septum, which is attached to the 

 supracondylar ridge and condyle of the humerus. These septa serve to separate the 

 muscles of the anterior from those of the posterior brachial region. The external 

 intermuscular septum extends from the lower part of the anterior bicipital ridge, 

 along the external supracondylar ridge, to the outer condyle ; it is blended with the 

 tendon of the Deltoid, gives attachment to the Triceps behind, to the Brachialis 

 anticus, Supinator longus, and Extensor carpi radialis longior, in front, and is 



