THE SUBCLAVIAN ARTERIES. 579 



Relations. It is covered, in front, by the skin, the superficial fascia, the 

 Platysma, deep cervical fascia ; by the clavicle, the Subclavius muscle and the 

 suprascapular artery and vein, and the transverse cervical vein ; the clavicular 

 descending branches of the cervical plexus and the nerve to the Subclavius muscle 

 pass vertically downward in front of the artery. The external jugular vein crosses 

 it at its inner side, and receives the suprascapular and transverse cervical veins, 

 which occasionally form a plexus in front of it. The subclavian vein is below the 

 artery, lying close behind the clavicle. Behind, it lies on the middle Scalenus 

 muscle; above it, and to its outer side, is the brachial plexus and Omo-hyoid mus- 

 cle ; below, it rests on the upper surface of the first rib. 



Peculiarities. The subclavian arteries vary in their origin, their course, and the height to 

 which they rise in the neck. 



The origin of the right subclavian from the innominate takes place, in some cases, above the 

 sterno-clavicular articulation, and occasionally, but less frequently, in the cavity of the thorax, 

 below that joint. Or 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 ves- 

 sel ; 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 toward the 

 right side, usually behind the 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 dorsal verte- 

 bra. 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 Scalenus. The 

 artery sometimes ascends as high as an inch and a half above the clavicle or an}' 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 

 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, 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 tyinir the third portion of the subclavian artery are as 

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



