24 Arteries of Head and Neck 



descending in front of that branch, distinguishes the spot with its middle 

 cervical or thyroid ganglion. 



The carotid sheath contains, in addition to the common and the 

 internal and carotid artery, the internal jugular vein and the pneumo- 

 gastric nerve, the vein being to the outer side of the artery, and the 

 nerve between and behind them. These three structures are separated 

 from each other by delicate fibrous partitions. The sheath receives a 

 considerable accession from the deep cervical fascia. 



The surgeon in seeking the artery should open the sheath upon the 

 inner, the arterial side, so as that the vein may not be in the way of 

 his needle. 



irregularities. The right common carotid artery may come from 

 a high or low division of the innominate, or as a separate branch from 

 the aortic arch. The two carotids may spring by a common trunk ; 

 or the left may come from the innominate, or from a left innominate 

 artery. The common carotid may divide as low as the cricoid carti- 

 lage, or may be continued as far as the hyoid bone. Sometimes the 

 common carotid gives off the superior thyroid branch. 



Relations of the common carotid in the neck. In front are 

 the skin, platysma, and fasciae ; the sterno-mastoid, and the beginning 

 of the sterno-hyoid and thyroid ; the omo-hyoid, which crosses at the 

 level of the fifth cervical vertebra ; the sterno-mastoid branch of the 

 superior thyroid artery, and the descendens noni lying upon the 

 sheath, as shown on page 27 ; the anterior jugular vein, and the 

 superior and middle thyroid veins running into the internal jugular. 



Behind are the lower cervical vertebrae, covered by the longus colli 

 and the rectus capitis anticus major. Additional posterior relations 

 are the inferior thyroid artery, winding upwards and inwards (p. 233) 

 from the subclavian; the sympathetic cord, and the recurrent laryngeal 

 nerve. 



Internally are the trachea and larynx, with a lobe of the thyroid 

 body and the inferior thyroid artery passing to it ; the oesophagus and 

 pharynx, and the recurrent laryngeal nerve ascending between the 

 trachea and oesophagus. Externally are the vagus and the internal 

 jugular vein. 



In the thorax. As the second part of the arch passes more from 

 before backwards than from right to left, and as the left carotid is 

 given off after the innominate and before the left subclavian, it neces- 

 sarily has the innominate a good deal in front of it and the subclavian 

 behind. 



Additional anterior relations are the origins of the sterno-hyoid and 

 sterno-thyroid muscles ; the left innominate vein, running obliquely 

 across to join in the formation of the superior cava ; and the remains 

 of the thymus gland, which, in the child, is a very important relation 

 so far as regards bulk (v. p. 155). 



Posteriorly are the trachea, oesophagus, and thoracic duct. 



