468 THE MUSCLES AND FASCIAE 



Relations. By its superficial surface, with the Latissimus dorsi below, and the long head of 

 the Triceps above. By its deep surface, with the Subscapularis, Latissimus dorsi, Coraco- 

 brachialis, short head of the Biceps brachii, 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 around its lower border, so that its tendon 

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



Nerves. The Supra- and Infraspinatus 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 glenoicTcavity. 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 pre- 

 venting displacement of the head of the humejuisup_wari3^~whll e the Infraspinatus and Teres 

 minor protect it behind, and prevent^HsIbcation ba^kwarcT. The Teres major assists the Latis- 

 simus dorsi in drawing the humerus downward and backward, when previously raised, and in 

 rotating it inward; when the arm is' fixed, it may assist the Pectoral and Latissimus dorsi muscles 

 in drawing the trunk forward. 



THE MUSCLES AND FASCIAE OF THE ARM. 



6. The Anterior Humeral Region (Fig. 349). 



Coracobrachialis. 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 clavicle 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. 346). 



The deep fascia (fascia brachii) 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, and it is also continuous with 

 the axillary fascia. It forms a thin, loose, membranous sheath investing the muscles 

 of the arm, sending down septa between them, and is composed of fibres disposed 

 in a circular or spiral direction, and connected by vertical and oblique fibres. 

 It differs in thickness at different parts, being thin over the Biceps brachii, 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 supracon- 

 dylar ridge and to the 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 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, Brachioradialis, and Extensor carpi radialis longior in front. It is 

 perforated by the musculospiral nerve and the anterior terminal branch of the 

 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 supracondylar ridge to the inner condyle; 

 it is blended with the tendon of the Coracobrachialis, and affords attachment to 

 the Triceps behind, and the Brachialis anticus in front. It is perforated by the 

 ulnar nerve and the inferior profunda and anastomotica magna arteries. At 



