518 THE BLOOD-VASCULAR SYSTEM. 



right side, usually behind the trachea, oesophagus, and right carotid, sometimes between the 

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

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

 sal vertebra. Occasionally it perforates the anterior Scalenus ; more rarely it passes in front of 

 that muscle. Sometimes the subclavian vein passes with the artery behind the Anterior Scalene. 

 The artery may ascend as high as an inch and a half above the clavicle or any intermediate 

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

 higher than the left. 



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



Surface Marking. The course of the subclavian artery in the neck may be mapped out 

 by describing a curve, with its convexity upward at the base of the posterior triangle. The inner 

 end of this curve corresponds to the sterno-clavicular joint, the outer end to the centre of the 

 lower border of the clavicle. The curve is to be drawn with such an amount of convexity that 

 its mid-point reaches half an inch above the upper border of the clavicle. The left subclavian 

 artery is more deeply placed than the right in the first part of its course, and, as a rule, does not 

 reach quite as high a level in the neck. It should be borne in mind that the posterior border of 

 the Sterno-mastoid muscle corresponds to the outer border of the Scalenus anticus, so that the 

 third portion of the artery, that part most accessible for operation, lies immediately external to 

 the posterior border of the Sterno-mastoid. 



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

 examined, the student should direct his attention to a consideration of the best position in which 

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

 cases of aneurism or wound. 



Compression of the subclavian artery is required in cases of operations about the shoul- 

 der, 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 

 upper 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, should press with his 

 thumb in the angle formed by the posterior border of the Sterno-mastoid with the upper border 

 of the clavicle, downward, backward, and inward against the rib ; if from any cause the shoulder 

 cannot be sufficiently depressed, pressure may be made from before backward, so as to compress 

 the artery against the middle Scalenus and transverse process of the seventh cervical vertebra. 

 In appropriate cases, a preliminary incision may be made through the cervical fascia, and the 

 finger may be pressed down directly upon the artery. 



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

 the axilla, or in cases of aneurism on the cardiac side of the point of ligature; and the third part 

 of the artery is that which is most favorable for an operation, on account of its being compara- 

 tively superficial and most remote 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 pushed up by 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 circumstances 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 the clavicle is displaced, these variations will necessarily make the opera- 

 tion 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 

 follows : The patient being placed on a table in the supine position, with the head drawn over to 

 the opposite side and the shoulder depressed as much as possible, the integument should be 

 drawn downward over the clavicle, and an incision 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 inner end of the preceding. The object in drawing 

 the skin downward is to avoid any risk of wounding the external jugular vein, for as it perforates 

 the deep fascia above the clavicle, it cannot be drawn downward with the skin. The soft parts 

 should now be allowed to glide up, and the cervical fascia should be divided upon a director, 

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

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

 will now be seen toward the inner side of the wound: this and the suprascapular and transverse 

 cervical veins, which terminate in it, should be held aside. If the external jugular vein is at all 

 in the way and exposed to injury, it should be tied in two places and divided. The suprascapu- 

 lar artery should be avoided, and the Omo-hyoid muscle held aside if necessary. In the space 

 beneath this muscle careful search must be made for the vessel : a deep layer of fascia and some 

 connective tissue having been divided carefully, the outer margin of the Scalenus anticus muscle 

 must be felt for, and, the finger being guided by it to the first rib, the pulsation of the subcla- 

 vian artery will be felt as it passes over the rib. The sheath of the vessels having been opened, 

 the aneurism needle may then be passed around the artery from above downward and inward, so 

 as to avoid including any of the branches of the brachial plexus. If the clavicle is so raised by 

 the tumor that the application of the ligature cannot be effected in this situation, the artery may 

 be tied above the first rib, or even behind the Scalenus anticus muscle ; the difficulties of the 

 operation in such a case will be materially increased, on account of the greater depth of the artery 

 and the alteration in position of the surrounding parts. 



