SURGICAL AXATOMY OF SUBCLAVIAN ARTERIES. 893 



important parts, and the large size cf its branches, render operations on this 

 vessel peculiarly difficult. 



The third division of the artery, situated beyond the anterior scalenus muscle 

 is the part which is most favourably circumstanced for the application of a 

 ligature. Here the vessel is nearest to the surface, and most remote from the 

 origui of the large branches. The subclavian artery is generally most easy of 

 access above the clavicle while the parts are in their natural position, but when 

 they are displaced by an aneurism in the axilla, the clavicle may be so much 

 elevated by the tumoiu-, as to be placed in front of the vessel, or even above it ; 

 and such a condition may requu'e special modifications of the operation. 



In the operation of jaassing a ligature round the third part of the subclavian 

 artery, an incision is to be made a little above the most prominent or convex 

 part of the clavicle, opposite the place where the vessel lies, and parallel with it. 

 By di-awing the integument downwards over the clavi«le, the parts covering the 

 bone may be divided with freedom. 



Along with the integument, the platysnia and several nerves are divided in 

 this incision, but no vessel is endangered, except in those rare cases in which the 

 cephalic vein or the external jugular crosses over the clavicle. It will, in most 

 cases, be an advantage to add a short vertical incision, dii-ected downwards to 

 the middle of the horizontal one. Should the sterno-mastoid muscle be broad at 

 its lower end, or should the interval between that muscle and the trapezius be 

 insufficient for the farther steps of the operation, a portion of the former muscle, 

 or even of both muscles, must be divided. 



The external jugidar vein, joined by the veins from the shoulder, is usually 

 over the artery, and it must be held aside, or it may be necessary to divide 

 it. If divided, the lower end of the vessel requires the application of a liga- 

 ture as well as the upper one, in consequence of the reflux of blood from the 

 subclavian vein. The omo-hyoid muscle will also be turned aside if necessary. 

 At this stage of the operation, in the usual position of the clavicle, the first rib 

 is the best guide to the vessel. At this place the brachial neiwes are close to the 

 vessel, so that great care must be exercised in passing the ligature round the 

 artery. But if it is found necessary to raise greatly the outer end of the clavicle, 

 then it will, in many cases, be more easy to place the ligature on the artery inside 

 the insertion of the scalenus muscle, or even behmd that muscle. Above the 

 first rib, the situation of the vessel may be ascertained by means of the brachial 

 nerves and the scalenus muscle ; and, before the membrane covering them is 

 divided, the position of these structui-es may be ascertained by the cord-like feel 

 of the nerves, and the smooth, flat form of the muscle. 



With reference also to the choice of the exact place at which the ligatui'e is to 

 be passed round this part of the artery, it should always be borne in mind that 

 -a very considerable branch may be given off from the main artery, immediately 

 beyond the scalenus muscle, or at some other part of the vessel. This branch is 

 most frequently one corresponding to the posterior scapular ; but in rarer cases 

 may be the superficial cervical or suprascapular. 



The second dicision of the suljolavian artcrij, or that situated behind the scalenus 

 anticus muscle, is the part which rises highest in the neck, and on this account 

 it may be advantageously selected for the application of a ligature when the 

 vessel is difficult of access beyond the muscle. The chief objection to operating 

 on this part of the artery arises from the contiguity of the large branches. Care 

 is necessary in dividing the scalenus muscle to avoid the i^hrenic nerve and the 

 internaA jugular vein. Moreover, the fact of the close apposition of the subcla- 

 vian artery with the pleura, except where it rests on the rib, must be borne in 

 mind. 



Difficulties also arise from the occurrence of an unusual position of the artery, 

 as when it passes through the substance of the anterior scalenus, or when it is 

 in front of that muscle ; but such cases are of very rare occvu-rence. 



Th? first part of the subclavian artery on the left side may be said to be 

 inaccessible for the application of a ligature, in consequence of its depth and its 

 close connection with the lung and other inaportant structures, such as the internal 

 jugular and left innominate veins. 



