BRANCHES OF THE SUBCLAVIAN ARTERY. 519 



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

 the neck, has been considered favorable for the application of the ligature when it is difficult to 

 tie the artery in the third part of its course. There are, however, many objections to the ope- 

 ration 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 ; and 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 

 proximity of so many of its large branches arising internal to this point must be a still further 

 objection to the operation. In cases, however, where the sac of an axillary aneurism encroaches 

 on the neck, it may be necessary to divide the outer half or two-thirds of the Scalenus anticus 

 muscle, so as to place the ligature on the vessel at a greater distance from the sac. The opera- 

 tion is performed exactly in the same way as ligature of the third portion, until the Scalenus 

 anticus is exposed, when it is to be divided on a director (never to a greater extent than its outer 

 two-thirds), and it immediately retracts. The operation is therefore merely an extension of liga- 

 ture of the third portion of the vessel. 



In those cases of aneurism of the axillary or subclavian artery which encroach upon the 

 outer portion of the Scalenus muscle to such an extent that a ligature cannot be applied in that 

 situation, it may be deemed advisable, as a last resource, to tie the first portion of the subcla- 

 vian artery. On the left side this operation is almost impracticable ; the great depth of the 

 artery from the surface, its intimate relation with the pleura, and its close proximity to the 

 thoracic duct and to so many important veins and nerves, present a series of difficulties which it 

 is next to impossible to overcome. 1 On the right side the operation is practicable, and has been 

 performed, though never with success. The main objection to the operation in this situation is 

 the smallness of the interval which usually exists between the commencement of the vessel and 

 the origin of the nearest branch. The operation may be performed in the following manner : 

 The patient being placed on the table in the supine position with the neck extended, an incision 

 should be made along the upper border of the inner part of the clavicle, and a second along 

 the inner border of the Sterno-mastoid, meeting the former at an angle. The attachment of 

 both heads of the Sterno-mastoid must be divided on a director and turned outward; a few 

 small arteries and veins, and occasionally the anterior jugular, must be avoided, or, if necessary, 

 ligatured in two places and divided, and the Sterno-hyoid and Sterno-thyroid muscles divided in 

 the same manner as the preceding muscle. After tearing through the deep fascia with the finger- 

 nail, the internal jugular vein will be seen crossing the subclavian artery ; this should be pressed 

 aside and the artery secured by passing the needle from below upward, by which the pleura is 

 more effectually avoided. The exact position of the vagus nerve, the recurrent laryngeal, the 

 phrenic and sympathetic nerves should be remembered, and the ligature should be applied near 

 the origin of the vertebral, in order to afford as much room as possible for the formation of a 

 cpagulum between the ligature and the origin of the vessel. It should be remembered that the 

 right subclavian artery is occasionally deeply placed in the first part of its course when it arises 

 from the left side of the aortic arch, and passes in such cases behind the ossophagus or between 

 it and the trachea. 



Collateral Circulation. After ligature of the third part of the subclavian artery the col- 

 lateral circulation is mainly established by three sets of vessels, thus described in a dissection : 



"I. A posterior set, consisting of the suprascapular and posterior scapular branches of the 

 subclavian, anastomosing with the subscapular from the axillary. 



" 2. An internal set produced by the connection of the internal mammary on the one hand, 

 with the superior and long thoracic arteries, and the branches from the subscapular on the 

 other. 



"3. A middle or axillary set, which consisted of a number of small vessels derived from 

 branches of the subclavian, above, and, passing through the axilla, terminated either in the 

 main trunk or some of the branches of the axillary below. This last set presented most con- 

 spicuously the peculiar character of newly-formed or, rather, dilated arteries, being excessively 

 tortuous, and forming a complete plexus. 



"The chief agent in the restoration of the axillary artery below the tumor was the sub- 

 scapular artery, which communicated most freely with the internal mammary, suprascapular, 

 and posterior scapular branches of the subclavian, from all of which it received so great an 

 influx of blood as to dilate it to three times its natural size." 2 



When a ligature is applied to the first part of the subclavian artery, the collateral circula- 

 tion is carried on by 1, the anastomosis between the superior and inferior thyroid ; 2, the anas- 

 tomosis of the two vertebrals ; 3, the anastomosis of the internal mammary with the deep 

 epigastric and the aortic intercostals ; 4, the superior intercostal anastomosing with the aortic 

 intercostals ; 5, the profunda cervicis anastomosing with the princeps cervicis ; 6, the scapular 

 branches of the thyroid axis anastomosing with the branches of the axillary ; and 7, the thoracic 

 branches of the axillary anastomosing with the aortic intercostals. 



1 The operation was, however, performed in New York by Dr. J. K. Rodgers, and the case is 

 related in A System of Surgery, edited by T. Holmes, 2d ed., vol. iii., pp. 620, etc. 



2 Guif s Hospital Reports, vol. i., 1836: case of axillary aneurism, in which Mr. Aston Key had 

 tied the subclavian artery on the outer edge of the Scalenus muscle twelve years previously. 



