UPPER EXTREMITY AND THORAX, ANTERIOR. 279 



circumflex is a small branch from the outside of the axillary 

 opposite the surgical neck of the humerus, around which it 

 turns, under the coracobrachialis and biceps muscles, to end 

 in the deltoid. At the bicipital groove it gives off a branch 

 (articular) which passes upward in the groove to the 

 shoulder-joint, (c) The posterior circumflex, nearly as 

 large as the subscapular, is given off the back of the axil- 

 lary, continues through the quadrilateral space formed by 

 the subscapularis, teres major, long head of triceps, and 

 humerus, with the circumflex nerve. For the continuation 

 of the artery see page 372. (d) The external mammary. 

 This is usually described as an abnormal branch, but is 

 found so frequently that it deserves a place with the more 

 constant branches of the axillary, from which it arises at 

 the lower margin of the axillary space and takes a course 

 downward, forward, and inward in the subcutaneous tissue 

 to the mammary region. 



Subscapularis. Fig. 63. 



Origin. From the inner two-thirds of the subscapular 

 fossa on the anterior surface of the scapula, from the lower 

 two-thirds of the axillary border of the same and inter- 

 muscular septum between it and the teres minor. 



Insertion. Into the lesser tuberosity of the humerus, the 

 surgical neck just below it, and into the capsule of the 

 shoulder-joint The nerve supply, from the first (upper) 

 and third (lower) subscapular nerves. 



Action. To rotate the humerus inward ; if the arm is 

 extended, to slightly adduct the humerus. When the 

 humerus is fixed it acts upon the scapula to turn it forward. 



Serratus Magnus. Figs. 63, 76. 



Origin. From the outer surfaces and upper margins of 

 the eight (or nine) upper ribs at their anterior and middle 



