394 ARTERIES. 



the artery may arise as a separate trunk from the arch of the aorta ; in such cases it may be 

 either the first, second, third, or even the last branch derived from that vessel: in the majority 

 of cases, it is the first or last, rarely the second or third. 



When it is the first branch, it occupies the ordinary position of the innominate artery; when 

 the second or third, it gains its usual position by passing behind the right carotid ; and when the 

 last branch, it arises from the left extremity of the arch, at its upper or back part, and passes 

 obliquely towards the right side, behind the oesophagus and right carotid, sometimes between the 

 oesophagus and trachea, to the upper border of the first rib, where it follows its ordinary course. 

 In very rare instances, this vessel arises from the thoracic aorta, as low down as the fourth dorsal 

 vertebra. Occasionally it perforates the Anterior scalenus ; more rarely it passes in front of this 

 muscle : sometimes the subclavian vein passes with the artery behind the Scalenus. The arterv 

 sometimes ascends as high as an inch and a half above the clavicle, or to any intermediate point 

 between this and the upper border of this bone, the right subclavian usually ascending higher 

 than the left. 



The left subclavian is occasionally joined at its origin with the left carotid. 



Surgical Anatomy. The relations of the subclavian arteries of the two sides having been 

 examined, the student should direct his attention to consider the best position in which compres- 

 sion of the vessel may be effected, or in what situation a ligature may be best applied in cases of 

 aneurism or wounds. 



Compression of the subclavian artery is required in cases of operations about the shoulder, in 

 the axilla, or at the upper part of the arm ; and the student will observe that there is only one 

 situation in which it can be effectually applied, viz., where the artery passes across the outer 

 surface of the first rib. In order to compress the vessel in this situation, the shoulder should be 

 depressed, and the surgeon, grasping the side of the neck, may press with his thumb in the hollow 

 behind the clavicle downwards against the rib ; if from any cause the shoulder cannot be suffi- 

 ciently depressed, pressure may be made from before backwards, so as to compress the artery 

 against the Middle scalenus and transverse process of the seventh cervical vertebra. 



Ligature of the subclavian artery may be required in cases of wounds of the axillary artery, or 

 in aneurism of that vessel ; and the third part of the artery is consequently that which is most 

 favorable for such an operation, on account of its being comparatively superficial, and most re- 

 mote from the origin of the large branches. In those cases where the clavicle is not displaced, 

 this operation may be performed with comparative facility ; but where the clavicle is elevated 

 from the presence of a large aneurismal tumor in the axilla, the artery is placed at a great depth 

 from the surface, which materially increases the difficulty of the operation. Under these circum- 

 stances, it becomes a matter of importance to consider the height to which this vessel reaches 

 above the bone. In ordinary cases, its arch is about half an inch above the clavicle, occasionally 

 as high as an inch and a half, and sometimes so low as to be on a level with its upper border. 

 If displacement of the clavicle occurs, these variations will necessarily make the operation more 

 or less difficult, according as the vessel is more or less accessible. 



The chief points in the operation of tying the third portion of the subclavian artery are as fol- 

 lows : The patient being placed on a table in the horizontal position, and the shoulder depressed 

 as much as possible, the integument should be drawn downwards upon the clavicle and an inci- 

 sion made through it upon that bone from the anterior border of the Trapezius to the posterior 

 border of the Sterno-mastoid, to which may be added a short vertical incision meeting the centre 

 of the preceding; the Platysma and cervical fascia should be divided upon a director, and if the 

 interval between the Trapezius and Sterno-mastoid muscles be insufficient for the performance 

 of the operation, a portion of one or both -may be divided. The external jugular vein will now be 

 seen towards the inner side of the wound ; this and the suprascapular and transverse cervical veins 

 which terminate in it should be held aside, and if divided both ends should be included in a ligature : 

 the suprascapular artery should be avoided, and the Omo-hyoid muscle must now be looked for, 

 and held aside if necessary. In the space beneath this muscle, careful search must be made for 

 the vessel ; the deep fascia having been divided with the finger-nail or silver scalpel, the outer 

 margin of the Scalenus muscle must be felt for, and the finger being guided by it to the first rib, 

 the pulsation of the subclavian artery will be felt as it passes over its surface. The aneurism 

 needle may then be passed around the vessel from before backwards, by which means the vein 

 will be avoided, care being taken not to include a branch of the brachial plexus instead of the 

 artery in the ligature. If the clavicle is so raised by the tumor that the application of the liga- 

 ture cannot be effected in this situation, the artery may be tied above the first rib, or even behind 

 the Scalenus muscle : the difficulties of the operation in such a case will be materially increased, 

 on account of .the greater depth of the artery, and alteration of the surrounding parts. 



The second division of the subclavian artery, from being that portion which rises highest 

 in the neck, has been considered favorable for the application of the ligature, where it is diffi- 

 cult to apply it in the third part of its course. There are, however, many objections to the 

 operation in this situation. It is necessary to divide the Scalenus anticus muscle, upon which 

 lies the phrenic nerve, and at the inner side of which is situated the internal jugular vein ; a 

 wound of either of these structures might lead to the most dangerous consequences. Again, the 

 artery is in contact, below, with the pleura, which must also be avoided ; and, lastly, the prox- 

 imity of so many of its larger branches arising internal to this point, must be a still further 



