BRANCHES OF THE SUBCLAVIAN ARTERY. 



581 



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

 other. 



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 funning 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.' l 



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- 

 Kimosis of the two vertebrals ; 3. the anastomosis of the internal mammary with the deep 

 epitrastrie 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. 



BRANCHES OF THE SUBCLAYIAX ARTERY. 



These are four in number. On the left side all four branches, the vertebral, 

 the int>-rn>tl. mammary, the thyroid axis, and the superior intercostal, generally 

 arise from the first portion of the vessel ; but on the right side the superior inter- 

 costal 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 ^ca- 

 lenus anticus. in the majority of cases a free interval of half an inch to an inch 

 existing between the commencement of the 

 artery and the origin of the nearest branch ; 

 in a smaller number of cases an interval 

 of more than an inch exists, never exceed- 

 ing an inch and three-quarters. In a very 

 few instances the interval had been found 

 to be less than half an inch. 



The Vertebral Artery (Fig. 352) is gen- 

 erally the first and largest branch of the 

 subclavian : it arises from the upper and 

 back part of the first portion of the vessel, 

 and. passing upward, enters the foramen 

 in the transverse process of the sixth cerv- 

 ical vertebra. 2 and ascends through the for- 

 amina in the transverse processes of all the 

 vertebrae above this. Above the upper bor- 

 der of the axis it inclines outward and upward to the foramen in the transverse 

 process of the atlas, through which it passes ; it then winds backward behind its 

 articular process, runs in a deep groove on the upper surface of the posterior 

 arch of this bone. and. passing beneath the posterior occipito-atlantal ligament, 

 pierces the dura mater and enters the skull through the foramen magnum. It 

 then passes forward and upward to the front of the medulla oblongata, and unites 

 with the vessel of the opposite side at the lower border of the pons Varolii to 

 form the baxilar '//////. 



Relations. At its origin it is situated behind the internal jugular vein and 

 inferior thyroid artery : and near the spine it lies between the Longus colli and 

 Scalenus anticus muscles, having the thoracic duct in front of it on the left side. 

 Within the foramina formed by the transverse processes of the vertebrae it is 

 accompanied by a plexus of nerves from the inferior cervical ganglion of the 

 sympathetic, and is surrounded by a dense plexus of veins which unite to form the 



1 Guy'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. 



2 The vertebral artery sometimes enters the foramen in the transverse process of the fifth ver- 

 tebra. Dr. Smyth, who tied this artery in the living subject, found it, in one of his dissections, pass- 

 ing into the foramen in the seventh vertebra. 



FIG. 360. Plan of the branches of the right 

 subclavian artery. 



