430 THE SUBCLAVIAN ARTEKIES. 



vessel, or even above it ; and such a condition may require special modifications of the 

 operation. 



In the operation of passing 1 a ligature round the third part of the subclavian artery, an 

 incision is made a little above and parallel to the middle third of the clavicle ; and in doing 

 this, if the integument be drawn downwards over the clavicle, the parts covering the bone 

 may be divided with freedom. 



Along with the integument, the platysma and some descending superficial nerves are 

 divided in this incision, but no vessel is endangered, except in those rare instances in which 

 the cephalic vein or the external jugular crosses over the clavicle. It will, in some cases, be 

 an advantage to add a short vertical incision, directed downwards to the middle of the 

 horizontal one. Should the clavicular attachment of the sterno-mastoid or trapezius 

 muscle be broader than usual, so that the interval between the two is insufficient 

 for the farther steps of the operation, a portion of one, or even of both muscles, must be 

 divided. 



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

 artery, and it must be held aside, or if necessary divided between two ligatures. The lower 

 end of the vessel requires the application of a ligature as well as the upper one, in conse- 

 quence of the reflux of blood from the subclavian vein, and the danger of air being drawn 

 into the circulation. The omo-hyoid muscle will also be drawn upwards if necessary, but as a 

 rule it is not exposed. The artery is now covered only by the areolar tissue of the supra- 

 clavicular fossa and a layer of the deep cervical fascia (upper part of the axillary sheath), 

 and in making the deeper dissection to reach the vessel, it will be best to divide these 

 structures cautiously with a director or some blunt instrument, in order to avoid wounding 

 the veins which pass inwards above the clavicle. At this stage of the operation the anterior 

 scalenus muscle should be sought for, as it forms the best guide to the artery. This will be 

 found descending nearly vertically behind the clavicular head of the sterno-mastoid, and if 

 the finger be carried down along the outer border of the muscle, it will pass over the front of 

 the artery, and reach the more or less prominent scalene tubercle on the upper surface of the 

 first rib, which in cases of difficulty is of service as a farther guide to the vessel. The part 

 of the artery to which the ligature is to be applied is placed above, and at the same time 

 somewhat to the outer side of and behind the tubercle. The nerves of the brachial plexus 

 are here very close to the artery, and great care is necessary in separating the lowest trunk 

 from the vessel. The artery is to be distinguished by its becoming flattened beneath the 

 finger, while the nerves have a rounded cord-like feel, and (in the living subject) by its 

 pulsation, although it is to be observed that this movement is frequently transmitted to the 

 adjacent nervous trunk owing to the close connection of the two structures. The needle 

 should be passed from behind forwards in order to avoid the nerves, as the vein is 

 placed at some little distance below and in front of this part of the artery, and ordinarily 

 does not come into view during the operation. The nerve to the subclavius may be exposed 

 on the front of the artery, and if so is to be carefully preserved, since it not unfrequently 

 furnishes an accessory root to the phrenic nerve. The latter nerve itself has also been seen 

 crossing the third part of the artery. 



With reference to the choice of the exact place at which the ligature is to be passed 

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

 a considerable branch is given off from the main trunk in the immediate neighbourhood of 

 the outer border of the scalenus muscle. This branch is most frequently the posterior 

 scapular ; but in rarer cases it may be the transverse cervical or suprascapular, or even the 

 internal mammary. 



The second division of the subclavian artery 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 objections to operating on this 

 part of the artery arise from the contiguity of the large branches, and its close connection 

 with the pleura. The steps of the operation are similar to those described above, but the 

 primary incision is made somewhat farther inwards, and it will be necessary to divide the 

 clavicular head of the sterno-mastoid and the scalenus anticus muscles. In doing this, care 

 must be taken not to injure the anterior jugular vein and the phrenic nerve, and it is farther 

 advisable not to carry the incision through the whole breadth of the scalenus, but to leave the 

 inner portion of the muscle undivided, in order to avoid wounding the internal jugular vein 

 or the branches of the thyroid axis. 



Difficulties may 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 occurrence. 



The 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 important structures, such as the internal jugular and innominate veins, and 

 the thoracic duct. 



