1 88 SURGICAL APPLIED ANATOMY. [Chap. xi. 



Emerging from the interval between the two teres 

 muscles, and winding horizontally round the shaft of 

 the humerus, quite close to the bone, and about the 

 line of the surgical neck, are the circumflex nerve and 

 posterior circumflex artery. This nerve affords an 

 example of an arrangement pointed out by Mr. Hilton, 

 viz., that a principal nerve to a joint not only supplies 

 the articular surfaces, but also some of the main 

 muscles that move that joint and the skin over those 

 muscles. This nerve supplies the shoulder joint, 

 the deltoid and teres minor muscles, and the skin over 

 the lower two-thirds of the shoulder and upper part 

 of the triceps. "The object of such a distribution of 

 nerves to the muscular and articular structures of a 

 joint, in accurate association, is to ensure mechanical 

 and physiological consent between the external 

 muscular or moving force and the vital endurance of 

 the parts moved, viz., of the joints, thus securing in 

 health the true balance of force and friction until 

 deterioration occurs" (Hilton). This nerve is frequently 

 damaged in injuries to the shoulder. It may be 

 severely bruised by a simple contusion of the part, 

 and this bruising may be followed by paralysis of the 

 deltoid. It would appear, however, that damage to 

 the circumflex is much less frequent after contusions 

 of the shoulder than was formerly maintained. It 

 will also be readily understood that the nerve is often 

 torn in fractures of the surgical neck of the humerus, 

 in dislocations of that bone (especially the luxation 

 backwards), and in violent attempts at reducing such 

 dislocations. The nerve, from its position, is very apt 

 to be seriously pressed upon by growths springing 

 from the upper end of the humerus. From its con- 

 nection with the joint, it follows that in chronic 

 inflammation of that part the inflammation may extend 

 along the nerve, producing a neuritis that may lead to 

 paralysis of the deltoid (Erb). 



