42 ANATOMY OF THE HEAD AND NECK. 



of the cervical plexus, called the communicans noni. The 

 descendens noni is sometimes found within the sheath 

 instead of upon it. 



Upon opening the carotid sheath, the relation of the 

 parts is to be carefully observed. The artery and vein are 

 separated from each other by a thin septum derived from 

 the sheath. The vein is the internal jugular vein, and lies 

 upon the outer side of the artery. Behind and between 

 the artery and vein will be found the pneumogastric or par 

 vagum nerve. Upon the inside of the artery the trachea 

 will be seen, and between the trachea and artery a medium- 

 sized nerve destined to the larynx, and called the recurrent 

 laryngeal. Between the artery and the transverse processes 

 of the cervical vertebrae, on which it rests, may be found 

 that part of the sympathetic nerve which connects the 

 cervical ganglia. Some small branches of the sj'mpathetic 

 nerve, being cardiac branches, should also be noticed in 

 connection with this view of the parts. 



The common carotid artery is of large size and uniform 

 calibre, and from its origin until its division opposite the 

 upper border, of the thyroid cartilage, gives off no branch 

 unless it be a small muscular twig. Its course is indicated 

 by a line drawn from the centre of the interval between the 

 mastoid process and the angle of the jaw to the steruo- 

 clavicular articulation ; this line corresponds to the ante- 

 rior border of the sterno-mastoid muscle, which is called the 

 guide to, or the satellite of, the artery. At the apex of the 

 triangle formed by the anterior belly of the omo-hyoid and 

 the anterior border of the sterno-mastoid muscles is the 

 u point of election" for placing a ligature upon the common 

 carotid artery. 



Having established these various relations, the dissection 

 may be continued by the examination of the muscles lying 

 upon the trachea. 



The STERNO-HYOID MUSCLE lies at the side of the median 

 line of the neck, being covered in at its lower part by the 

 sterno-mastoid, and is a thin ribbon-like muscle about an 

 inch in width, separated from its fellow of the other side 

 by a slight cellular interval. It arises from the internal 

 surface of the first bone of the sternum by a flat muscular 

 origin, and is inserted into the lower border of the body 

 of the hyoid bone. It is occasionally marked by trans- 

 verse tendinous intersections. It lies upon the stern o- 

 thyroid and thyro-hyoid muscles. 



