THE SUBCLAVIAN REGION. 93 



tioii upon that vessel, but from its actual position and 

 natural boundaries it would be more correctly termed 

 supra-clavicular. The hollow which exists above and 

 behind the clavicle is almost invariably well marked, 

 even where there is much fat in the neck ; and it is this 

 space, with its numerous contents and varying confor- 

 mation, which is of such surgical import. It is bounded 

 anteriorly by the posterior border of the sterno-cleido- 

 mastoid ; behind, by the rounded anterior border of the 

 trapezius -these muscles nearly meet above at their cra- 

 nial attachment, where their aponeuroses are blended ; 

 below by the clavicle, and above by the crossing of the 

 posterior belly of the omo-hyoid, and its floor is formed 

 by the first rib and the muscular structures attached 

 to it. 



The pulsation of the subclavian artery can be felt at 

 the bottom of the space as it crosses the first rib, against 

 which it can be readily controlled for any operation 

 about the shoulder or arm. The positions of the scalene 

 muscles, the cords of the brachial plexus, particularly 

 those of the fifth and sixth, and the course of the omo- 

 hyoid, are also felt, and generally to be seen, as emi- 

 nences beneath the integument. It must be borne in 

 mind that the " triangle" formed by the crossing of the 

 omo-hyoid is a result of dissection, and the detachment 

 of its aponeurosis ; no such regular interspace existing 

 during life, the inner border of the muscle lying behind 

 the clavicle, and its upper border only being seen whilst 

 in action. The change in the appearance of the hollow 

 immediately above and behind the clavicle is noticeable 

 under certain circumstances; thus, in inspiration, it is 

 considerably deepened, and during expiration becomes 

 flatter, when the pulse in the subclavian vein is gener- 



