754 



HUMAN ANATOMY. 



metry is retained ; but, since a portion of the original right aortic arch is included in 

 the adult right subclavian, this vessel is a little more than equivalent to its fellow 

 of the opposite side. Furthermore, since the innominate stem ascends directly 

 upward from its origin, a topographical asymmetry of the two vessels results. 



The origin of the right subclavian is opposite the right sterno-clavicular articula- 

 tion, and from that point the artery ascends upward and outward in a gentle curve 

 over the dome of the pleura to the inner border of the scalenus anticus. The origin 

 of the left subclavian is from the termination of the transverse portion of the aortic 

 arch, and is consequently much deeper in the thorax (Fig. 690). From its origin 

 it ascends at first almost vertically and then curves outward and slightly forward to 

 reach the inner border of the scalenus anticus. From this point onward the course of 

 the two arteries is the same. Passing behind the anterior scalene muscle, each artery 

 continues its course outward across the root of the neck, curving downward to the 

 outer border of the first rib, at which point it becomes known as the axillary artery. 



Fig. 701. 





Trapezius 



Descending 

 branches of 

 cervical plexus 



Transverse 

 cervical vessels 



Oino-hyoid 



muscle 



Brachial plexus 7 

 Suprascapular 



Subclavian artery 



Subclavian vein 



Clavicular portion of 

 sterno-mastoid 



External jugular vein 



Anterior scalene muscle 



Phrenic nerve 



Internal jugular vein 

 Sternal portion of 



sterno-mastoid 

 Common carotid artery 



■Sterno-hyoid muscle 

 First rib 



Clavicle 



Dissection of neck, showing relations of blood-vessels and nerves ; clavicle 

 disarticulated from sternum and drawn down. 



In consequence of the difference in origin, the right subclavian artery is usually 

 approximately 7.5 cm. (3 in.) in length, or about one inch shorter than the left. 

 In its course across the root of the neck the height which the subclavian artery 

 may reach varies considerably in different individuals ; in some it never rises above 

 the clavicle, while in others its highest point may be from 2.5-3 cm. (i-i^ in.) 

 above that bone. Most frequently it reaches a point about 1.5 cm. (^ in. ) above the 

 clavicle, this highest point being reached as it passes beneath the scalenus muscle. 

 As it commences its downward course towards the first rib, the artery undergoes a 

 more or less pronounced diminution in diameter, which persists for a distance of from 

 0.5-1 cm., and is followed by an enlargement to about its original size, what has 

 been termed an arterial isthmus and spindle thus resulting (page 720). 



Relations. — For convenience in description, the subclavian artery is usually 

 regarded as consisting of three portions. The first portion extends from its origin 

 to the inner edge of the scalenus anticus, the second portion lies behind that muscle, 



