82 



THE SUPERIOR EXTREMITY 



border of the scapula, anterior to the teres minor, and enters 

 the infraspinous fossa. 



The boundaries of the quadrangular space, as seen from 

 the front, are the subscapularis above, the teres major 

 below, the long head of the triceps medially, and the 

 surgical neck of the humerus laterally. At the back the 

 teres minor replaces the subscapularis as the upper boundary. 

 Between the subscapularis anteriorly, and the teres minor 

 posteriorly, the inferior surface of the capsule of the shoulder- 

 joint forms the upper boundary of the space, and through the 

 space, directly below the capsule, pass the axillary nerve and 

 the posterior humeral circumflex vessels. 



Arterise Circumflexse Humeri (O.T. Circumflex Arteries). 

 The posterior humeral circumflex artery has been already 



AA 



H. Transverse section of the 

 humerus immediately distal 

 to the tubercles. 

 A, A. Axillary artery. 

 P.C. Posterior circumflex artery 



of the humerus. 

 A.C. Anterior circumflex artery of 



the humerus. 

 C.N. Axillary nerve. 



a. Articular branch. 

 T.M. Branch to teres minor. 

 C. Cutaneous branches. 



FIG. 37. Diagram of the Circumflex Vessels and the Axillary Nerve. 



observed to arise, within the axilla, from the posterior aspect 

 of the axillary artery, a short distance distal to the subscapular 

 branch. It at once passes backwards, through the quadri- 

 lateral space, and, winding round the surgical neck of the 

 humerus, it is distributed in numerous branches to the deep 

 surface of the deltoid muscle. Several twigs are given also to 

 the shoulder-joint and the integument. It anastomoses with 

 the acromial branch of the thoraco-acromial artery and with 

 the anterior humeral circumflex artery, and also, by one or 

 more twigs, which it sends distally to the long head of the 

 triceps, with the profunda branch of the brachial artery. 



The termination of the anterior humeral circumflex artery 

 can now be more satisfactorily studied, and its anastomosis 



