Vertebral Artery 



231 



as the second or third trunk of the aorta, and reaches the scalenus by 

 winding behind the trachea and oesophagus. Sometimes the artery 

 passes in front of the scalenus anticus, and sometimes the vein passes 

 behind the muscle. 



Compression of the subclavian may be effected by the surgeon 

 standing behind the patient, gripping the shoulder with his fingers, 

 and thrusting the thumb towards the first rib, down the outer border 

 of the sterno-mastoid, the shoulder and clavicle having been first drawn 

 down. In certain cases it may be expedient to compress the artery by 

 the aseptic finger introduced through an incision in the deep fascia. 



Collateral circulation after ligation of the third part is carried on 

 by the service of the empty 

 branches of the axillary 

 artery. Thus, the superior 

 thoracic, acromial thoracic, 

 the long and the alar tho- 

 racic branches, and the 

 ending of the subscapular 

 bring blood from the supe- 

 rior intercostals, and from 

 intercostal branches of the 

 aorta and internal mam- 

 mary. The dorsalis scap- 

 ulae would help by its anas- 

 tomosis with the supra- 

 and posterior scapular 

 arteries, and the acromial 

 thoracic and the posterior 

 circumflex by their com- 

 munications with the 

 supra-scapular in the acro- 

 mial region. 



The branches vi the first 

 part are the vertebral, in- 

 ternal mammary, and thy- 

 roid axis ; from the second 

 part comes the superior 

 intercostal. 



The vertebral, arising 

 from the upper and back 

 part of the first portion, 

 makes a short ascent into 



the transverse process of Inosculations of subclavi , n artery . (H OL DEN .) 

 the sixth cervical vertebra ; 



it then passes through the transverse processes above this, and, taking 

 a peculiarly twisted course near the posterior ring of the atlas, enters 



