DISSECTION OF THE NECK 333 



the ventral and lateral surfaces by the wide thyroid cartilage, 

 which forms a prominent swelling in the throat, placed 

 between the rami of the mandible and readily identified by the 

 finger. Behind this is the annular cricoid cartilage, which is 

 wide dorsally and narrow ventrally. Behind the cricoid the 

 trachea narrows slightly, and is surrounded 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. 



C. 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. 



D. The Muscles of the Neck. 



A few of the more prominent of the ventral muscles of the 

 neck are alone described here. 



1. The sterno-mastoid muscles are a pair of narrow but 



strong muscular bands, which arise from the anterior 

 end of the sternum, close to the middle line, and run 

 obliquely forwards and outwards, across the front of 

 the neck, to be inserted into the mastoid processes of 

 the skull immediately behind the ears. 



Cut through the right sterno-mastoid close to its origin 

 from the sternum, and turn it forwards. Near its anterior 

 end, note, and carefully preserve, a branch of the spinal 

 accessory nerve, which enters the muscle on its inner side, 

 about half an inch behind the angle of the jaw. 



2. The sterno-hyoid muscles are a pair of broad but thin 



muscular bands, running along the ventral surface 

 of the neck. They arise from the dorsal surface of 

 the anterior end of the sternum, where the two are 

 fused, and run forwards along the neck. A little 



