THE HEAD AND NECK lo8i 



jugular vein crosses the stemo-cleido-mastoid muscle in the direc- 

 tion of a line extending from a point just behind the angle of the 

 inferior maxilla to a point above the centre of the cla\'icle, and it is 

 accompanied by the superficial cervical glands. The common 

 carotid artery lies under cover of the anterior border of the stemo- 

 cleido-mastoid muscle, in the direction of a line drawn from the 

 stemo-clavicular joint to a point midway between the angle of the 

 inferior maxilla and the tip of the mastoid process of the temporal 

 bone. The vessel extends along this line as high as the level of the 

 upper border of the thyroid cartilage, and thereafter it is replaced 

 by the external carotid artery. The internal jugular vein is close 

 to the outer side of the common carotid artery, and the pneumo- 

 gastric ner\-e lies deeply between the two vessels. If deep pres- 

 sure is made over the common carotid artery, on a level with the 

 cricoid cartilage of the larynx, the tubercle of the costal process of 

 the sixth cervical vertebra (commonly spoken of as the anterior 

 tubercle of the transverse process) may be felt. It is known as the 

 carotid tubercle of Chassaignac. 



The commencement of the right innominate vein and the bifurca- 

 tion of the innominate artery' lie behind the upper border of the 

 right stemo-cla\4cular joint ; and the commencement of the left 

 innominate vein and the left common carotid artery lie behind the 

 left stemo-clavicular joint. Near the middle line of the neck the 

 anterior jugular vein descends vertically. The spinal portion of 

 the spinal accessory nerve passes downwards and outwards beneath 

 the anterior border of the stemo-cleido-mastoid to pierce the deep 

 part of that muscle at about the junction of the upper fourth and 

 lower three-fourths. The ner\'e is met with fuUy i inch below the 

 tip of the mastoid process, and in the direction of a line let fall 

 vertically from the mastoid tip. It is very nearly on a level with 

 the body of the hyoid bone. Along the posterior border of the 

 stemo-cleido-mastoid the IjTnphatic glands, known as the glandulae 

 concatenatae, may be felt. 



Important structures occupy the middle line of the neck, 

 and can be usually distinguished without difficulty. These are 

 as follows, in order from above downwards : (i) the body of the 

 hyoid bone, lying just below the inferior maxilla, and having the 

 great comu projecting backwards and upwards on either side ; 

 (2) the thyro-hyoid membrane ; (3) the th\Toid cartilage, with its 

 prominent angle or isthmus (pomum Adami) in the middle line, 

 leading up to the V-shaped thyroid notch on the upper border, and 

 its expanded ala on either side, each of which terminates posteriorly 

 in a superior and an inferior comu ; (4) the crico-thjToid membrane ; 

 (5) the narrow, anterior part of the cricoid cartilage, which coincides 

 with the level at which the anterior belly of the omo-hyoid muscle 

 crosses the carotid sheath : and (6) the rings of the trachea, which, 

 however, are covered superiorly by the isthmus of the thjToid body, 

 and inferiorly by the stemo-hyoid and stemo-thyroid muscles and 

 adipose tissue. 



