PLATE XIII. 



THE CIRCUMFLEX NERVE AND SCAPULAR 

 QUADRILATERAL. 



In this dissection the attachment of the deltoid to the spine of the scapula has been 

 eut through and the spine sawn across at its junction with the acromion process ; the 

 whole muscle and bone were then turned outwards, to expose the circumflex nerve and 

 posterior circumflex artery. 



When viewed from the back, with the arm abducted from the side, the quadrilateral 

 space or scapular quadrilateral is formed by the bone above, the long head of the triceps 

 below, externally by the teres major, and the teres minor internally ; but seen from the 

 front, the teres minor is replaced by the axillary border of the subscapularis. Coming 

 through the space are the posterior circumflex vessels and circumflex nerve. 



The branch of the circumflex artery marked (g) passes down to anastomose with 

 one from the superior profunda, and it is this branch that usually enlarges and takes 

 the place of the circumflex when, in abnormal conditions, that artery is not given off 

 from the axillary, or vice versd. 



The circumflex nerve is a good illustration of Hilton's law, that the main nerve 

 to a joint not only supplies it, but also some of the muscles which act on the joint, 

 as well as the skin over those muscles, thus securing during movement the true balance 

 of force and friction. 



The fibres of origin of the infra-spinatus from the spine of the scapula overlap the 

 upper portion of the origin from the infra-spinous fossa. 



