DISSECTION OF THE NECK. 363 



the neck almost in the middle line. It is only partially 

 exposed at present, but will be seen better in the course of the 

 dissection. Its anterior end, the larynx, which lies almost 

 immediately behind the hyoid, is dilated, and surrounded on 

 its ventral and lateral surfaces by the wide thyroid cartilage, 

 which forms a prominent median swelling in the throat, 

 between the rami of the mandible. Behind this is the 

 annular cricoid cartilage, which is wide dorsally and narrow 

 ventrally. Behind the cricoid the trachea narrows slightly, and 

 is strengthened by a series of cartilaginous rings, incomplete 

 along the mid-dorsal line. The trachea runs backwards along 

 the neck, and, entering the thorax, divides about the level of 

 the middle of the heart into the right and left bronchi, which 

 enter the right and left lungs respectively. 



E. The Thyroid Body. 



The thyroid is a soft vascular body, consisting of a pair of 

 lateral lobes at the sides of the anterior part of the trachea, 

 connected by a narrow median lobe, which runs across the 

 ventral surface of the trachea a short way behind the thyroid 

 cartilage. 



F. The Nerves of the Neck. 



Expose and clean the following nerves on either the right 

 or the left side of the neck. 



1. The spinal accessory nerve, the eleventh cranial nerve, 

 leaves the skull by the foramen lacerum posterius, 

 between the auditory capsule and the ex-occipital 

 bone, in company with the pneumogastric and glosso- 

 pharyngeal nerves. Outside the skull it runs almost 

 vertically downwards for about half an inch, and 

 then divides into branches distributed to the sterno- 

 mastoid and other muscles. 



The branch to the sterno-mastoid has already been seen 

 (p. 861). Follow this bach to its junction with the main stem 

 of the nerve, and then trace this latter up to the base of the 

 skull. 



