THE LAKYNX. 869 



gence of this nerve from the neural canal, and runs 

 back alongside the vertebral column. Entering the 

 thorax it continues its course backwards, lying 

 between the heart and the lungs, and ends in the 

 diaphragm, which it supplies with motor fibres. 



In the neck it crosses the roots of the hinder 

 cervical nerves almost at right angles. It receives 

 a small branch from the fifth cervical nerve, and 

 sometimes one from the sixth, as it passes them. 



To expose the phrenic nerve gently press the heart and 

 lung apart. Folloio the nerve hack to the diaphragm, and 

 forwards along the neck to its origin. 



G. The Larynx. 



The larynx, or organ of voice, is the anterior part of the 

 trachea. The thyroid and cricoid cartilages form its outer 

 wall, and it is protected in front by the epiglottis. 



Make a medium longittidinal section through the anterior 

 part of the trachea. 



1. The epiglottis is a curved plate of cartilage covered by 



mucous membrane, attached to the anterior and 

 ventral border of the larynx. When food is being 

 swallowed it closes over the glottis like a lid, pre- 

 venting the passage of the food into the larynx. 



2. The thyroid cartilage forms the most anterior ring of 



the trachea : it is about half an inch in length along 

 the mid- ventral line, but is incomplete dorsally. 



3. The cricoid cartilage, or second ring of the trachea, is a 



complete ring, lying immediately behind the thyroid. 

 It is narrow ventrally, but wide dorsally; and articu- 

 lates with the postero-dorsal angles of the thyroid 

 cartilage. 



4. The arytenoid cartilages are a pair of cartilaginous 



nodules, articulated to the anterior edge of the dorsal 

 surface of the cricoid cartilage. 



5. The ventricles of the larynx are a pair of shallow 



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