THE NECK, ANTERIOR. 101 



Action. They flex the neck laterally if acting from 

 below ; if from above, they raise and fix the first rib, thus 

 aiding inspiration. 



Scalenus Posticus. Fig. 76. 



Origin. From the posterior tubercles of the transverse 

 processes of the lower two or three cervical vertebrae. 



Insertion. Into the outer surface of the second rib 

 behind the insertion of the serratus magnus. 



Nerve Supply. The three lower cervical nerves. 



Action. As slight lateral flexor of the lower cervical 

 vertebrae, also as an accessory muscle of inspiration by 

 raising and fixing the second rib. 



The Common Carotid Artery. Figs. 1 8, 71. 



On the right side the common carotid extends from the 

 bifurcation of the innominate behind the sternoclavicular 

 articulation, upward to the level of the upper border of the 

 thyroid cartilage, where it divides into the external and 

 internal carotids. 



On the left side the artery arises as the middle branch 

 from the arch of the aorta. Its course is upward to the 

 same point as on the right side. 



Relations. The relations of the thoracic portion of the 

 left common carotid are given on page 340. 



In the neck they are alike. 



At the base of the neck the common carotids are about 

 an inch apart, at their termination about two inches apart. 



The course of the artery is indicated by the anterior bor- 

 der of the sternomastoid (natural landmark), or a line 

 drawn from the sternoclavicular articulation to the front of 

 the mastoid process (artificial). 



The common carotid, internal jugular, and pneumogas- 

 tric nerve are contained within the same sheath of the deep 



