THE A I? If. 475 



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

 in length, which is inserted into the internal 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 synovia! bursa. the two tendons 

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



Relations. By its posterior surface, with the integument, from which it is 

 separated, internally, by the Latissimus dorsi; and externally, by the long head 

 of the Triceps ; 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. 



Nerves. The Supra- and Infraspinatus muscles are supplied by the suprascap- 

 ular nerve ; the Teres minor, by the circumflex ; and the Teres major, by the 

 lower subscapular. 



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

 side, and fixes the head of the humerus in its socket. 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 it 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 displacement 

 of the head of the humerus downward, while the Infraspinatus and Teres minor 

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

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

 viouslv raised, and rotating it inward; when the arm is fixed, it mav assist the 



, / 



Pectoral and Latissimus dorsi muscles in drawing the trunk forward. 



THE AEM. 



Anterior Humeral Region (Fig. 303). 

 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. 301 ). 



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

 front of the great Pectoral muscle, 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 

 condyloid 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 external bicipital ridge, 

 along the external condyloid 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 

 perforated by the musculo-spiral nerve and superior profunda artery. The internal 

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

 the internal lip of the bicipital groove below the Teres major, along the internal 

 condyloid ridge to the inner condyle ; it is blended with the tendon of the Coracc- 

 brachialis. and affords attachment to the Triceps behind, and the Brachialis anticus 



