630 THE VASCULAR SYSTEMS 



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 oper- 

 ation is performed exactly in the same way as a ligation 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 

 ligation of the third portion of the vessel. 



In those cases of aneurism of the axillary or subclavian artery in which the aneurism encroaches 

 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 

 subclavian artery. On the left side this operation has been regarded as almost impracticable; 

 the great depth of the artery from its surface, its intimate relation with the pleura, and its close 

 proximity to the thoracic duct and to so many important veins and nerves, presents a series of 

 difficulties which it is very difficult to overcome. Nevertheless, it has been successfully done 

 several times. 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 Sternomastoid, meeting the former at an angle. The attachment of both heads of the 

 Sternomastoid must be divided on a director and turned outward; a few small arteries and 

 veins, and occasionally the anterior jugular vein, must be avoided, or, if necessary, ligated in 

 two places and divided, and the Sternohyoid and Sternothyroid muscles are to be divided in 

 the same manner as the preceding muscle. After tearing through the deep fascia, 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, the recurrent laryngeal, the phrenic and sympathetic 

 nerves should be remembered, and the ligature should be applied near the origin of the verte- 

 bral, in order to afford as much room as possible for the -formation of a coagulum 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 oesophagus or between it and the trachea. 



Branches. The branches given off from the subclavian artery are: 



Vertebral. Internal mammary. 



Thyroid axis. Superior intercostal. 



On the left side all four branches generally arise from the first portion of the 

 vessel, but on the right side the superior intercostal usually arises from the second 

 portion of the vessel. On both sides of the body the first three branches arise close 

 together at the inner margin of the Scalenus anticus: in the majority of cases a 

 free interval of from half an inch to an inch exists between the commencement 

 of the artery and the origin of the nearest branch. The vertebral artery 

 arises from the upper and posterior part of the subclavian artery, the iutewwl 

 Btstmst&cry fperna the* upper and peaterioc. part of- the subclwian artery, the 

 internal mammary from the lower part of the artery; the thyroid axis from in 

 front and the superior intercostal from behind. 



The vertebral artery, the first branch of the subclavian, is distributed entirely 

 to the head and neck, chiefly supplying the posterior portion of the brain. It 

 has been described on pages 621 to 625. 



The thyroid axis (truncus thyreocervicalis) (Figs. 438 and 459) is a short thick 

 trunk which arises from the fore part of the first portion of the subclavian artery, 

 close to the inner border of the Scalenus anticus muscle, and divides, almost 

 immediately after its origin, into three branches the inferior thyroid, suprascapular, 

 and transverse cervical. 



The inferior thyroid artery (a. thyreoidea inferior) (Fig. 438) passes upward, in 

 front of the vertebral artery and Longus colli muscle; then turns inward behind the 

 sheath of the common carotid artery and internal jugular vein, and also behind 



