I1I2 A MANUAL OF ANATOMY 



transverse processes as high as the level of the fourth ; the longus 

 colli, scalenus anticus, and part of the rectus capitis anticus major, 

 muscles ; the gangliated cord of the sympathetic, which is inti- 

 mately related to the posterior wall of the carotid sheath ; the 

 recurrent laryngeal nerve ; and the inferior thyroid artery, both of 

 which latter structures pass inwards and upwards behind the 

 lower part of the sheath. The carotid body lies behind the vessel 

 close to its bifurcation. 



External. — ^The internal jugular vein and the pneumogastric 

 nerve, the latter lying between the artery and the vein, on a 

 plane posterior to both. At the lower part of the neck, on the 

 right side, the internal jugular vein diverges from the common 

 carotid artery, so as to leave a slight interval^ in which the right 

 pneumogastric nerve appears as it is about to pass over the first 

 part of the right subclavian artery. On the left side, however, the 

 internal jugular vein is very closely related to the common carotid 

 artery, and more or less overlaps it. 



Internal. — From below upwards (i) the trachea and oesophagus, 

 with the recurrent laryngeal nerve and the inferior thyroid 

 artery lying in the intervening groove ; (2) the lateral lobe of 

 the thyroid body, upon which the vessel impresses a groove, and 

 by which it may be slightly overlapped ; and (3) the lar3mx and 

 pharynx. 



The common carotid artery, as a rule, gives off no branch. The 

 superior thyroid artery, however, may arise from it superiorly, 

 and in some cases the ascending pharyngeal artery. 



Surgery — Compression. — ^The part of the vessel most favourably 

 situated for compression lies in front of the tubercle of the costal 

 process of the sixth cervical vertebra, this tubercle, known as the 

 carotid tubercle of Chassaignac, being on a level with the cricoid 

 cartilage of the larynx. 



Ligation. — ^The part of the vessel most favourably placed for 

 ligation is situated on a level with the cricoid cartilage, just above 

 the point where it is crossed by the anterior belly of the omo-hyoid 

 muscle. The structures to be avoided in the operation are as 

 follows : (i) the descendens cervicis nerve, upon, or it may be 

 within, the sheath ; (2) the internal jugular vein and pneumogastric 

 nerve, both of which are within the sheath, and upon the outer side 

 of the artery ; and (3) the gangliated cord of the sympathetic, 

 which lies behind, and in close contact with, the sheath. The small 

 stemo-cleido-mastoid artery will probably be cut, as it passes 

 obliquely downwards and outwards over the sheath in the carotid 

 triangle. Ligation of the artery below the level of the cricoid 

 cartilage is attended with difficulty, the vessel being here covered 

 by the stemo-hyoid and stemo-thyroid muscles, in addition to 

 the platysma myoides and stemo-cleido-mastoid. On the left 

 side the internal jugular vein would constitute an additional 

 difficulty. 



Collateral Circulation after Ligation. — (r) Cross anastomoses take 



