THE ANTERIOR PART OF THE NECK 251 



forms the highest part or summit of the arch, and rises from 

 half an inch to an inch above the level of the clavicle. 



In this part of its course the vessel is not so deeply 

 placed. Anteriorly it is covered by (i) skin; (2) superficial 

 fascia and platysma; (3) deep fascia; (4) clavicular head 

 of the sterno-mastoid ; (5) scalenus anterior. The phrenic 

 nerve on the right side is also an anterior relation, but it is 

 separated from the artery by the medial margin of the 

 scalenus anterior. Posteriorly and inferiorly, the vessel is in 

 relation with the pleura, Sibson's fascia intervening. The 

 subclavian vein lies at a lower level than the artery and on 

 an anterior plane, and is separated from it by the scalenus 

 anterior. 



The third part of the subclavian artery is described on 

 p. 151. 



Branches of the Subclavian Artery. Four branches 

 spring from the subclavian trunk (Fig. 103). Three take 

 origin, as a general rule, from the first part of the artery 

 close to the scalenus anterior, and one from the second part. 

 They are 



1 1. Vertebral. 



f Inferior thyreoid 



*romtne J 2 Thyreo-cervical \ Transverse cervical 



(Transverse scapular. 

 \3. Internal mammary. 



From the f' ( Superior intercostal. 



second part. \ C( \ Deep cervical. 



In a great number of cases a branch of considerable size will be 

 observed springing from the third part of the subclavian artery. This, 

 in all probability, is the descending branch of the transverse cervical, 

 arising directly from the subclavian. It is so common an occurrence that 

 the dissector must always be prepared to meet it. 



Arteria Vertebralis. This is the first branch which is 

 given off by the subclavian. It springs from the upper and 

 posterior aspect of the trunk about a quarter of an inch from 

 the medial margin of the scalenus anterior on the right side, 

 and from the point where the vessel reaches the root of the 

 neck on the left side. Only a small portion of it is seen in 

 the present dissection. It proceeds upwards in the interval 

 between the longus colli and the scalenus anterior muscles, 

 posterior to the common carotid, and disappears into the 

 foramen transversarium of the transverse process of the sixth 

 cervical vertebra. It is placed very deeply, and is covered 



