THE LAEYNX 339 



a small branch from the fifth cervical nerve, and 

 sometimes one from the sixth, as it passes them. 

 Press the heart and right lung gently apart to expose the 



phrenic nerve. Follow the nerve back to the diaphragm, and 



forwards along the neck to its origin. 



Gr. The Larynx. 



The larynx, or organ of voice, is formed by the anterior 

 part of the trachea. The thyroid and cricoid cartilages form 

 its outer wall, and it is overhung in front by the epiglottis. 



Make a median longitudinal section through the anterior 

 part of the trachea. 



1. 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. 



2. 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. 



3. The arytenoid cartilages are a pair of cartilaginous 



nodules, articulated to the anterior edge of the dorsal 

 surface of the cricoid cartilage. 



4. The ventricles of the larynx are a pair of shallow lateral 



depressions of the mucous membrane of the inner 

 surface of the larynx. 



5. The vocal cords are a pair of folds of mucous membrane, 



strengthened by elastic ligaments, and forming the 

 posterior lips of the ventricles. They are attached 

 dorsally to the arytenoids, and at their ventral ends 

 to the thyroid cartilage. It is by their vibration 

 that the voice is produced, 



6. The glottis is the narrow vertical slit between the vocal 



cords, through which the air passes to and from the 

 lungs. 



7. The false vocal cords are folds of mucous membrane 



similar to the vocal cords, which form the anterior 

 boundaries of the ventricles. 



z2 



