2 98 VERTEBRATE ZOOLOGY 



the larynx from the pharynx, is a slit in the floor of the pharynx ; 

 in front of it is the epiglottis, an elevated cartilaginous structure, 

 ventral in position, which guards the opening. The larynx, which 

 controls the passage of air into and from the lungs and produces 

 the voice, is made up of plates of cartilage connected by ligaments 

 and muscles. There are three large unpaired cartilages,— the 

 thyroid, cricoid, and epiglottis,— and a pair of small cartilages, the 

 arytenoids. The thyroid cartilage is a large plate ventral and 

 lateral in position; it forms what is known as " Adam's apple" in 

 the human throat. The cricoid cartilage lies just behind it and 

 forms a complete ring which is wide dorsally and narrow ventrally. 

 The arytenoids, which support the opening of the glottis, are two 

 minute bodies which articulate with the anterior edge of the 

 dorsal side of the cricoid cartilage. 



Just within the glottis will be seen, on the inner surface of the 

 larynx, a pair of fleshy ridges which extend from the arytenoid 

 cartilages ventrally to the thyroid cartilage ; these are the vocal 

 cords, the vibration of which produces the voice. 



Study the trachea, the bronchi (which are formed by the branch- 

 ing of the hinder end of the trachea), and the lungs. The carti- 

 laginous rings of the trachea are incomplete on the dorsal side, 

 where it lies against the oesophagus. The structure of the bronchi 

 is similar to that of the trachea. The lungs are large-lobed organs, 

 a branch of the bronchus extending into each lobe. Dissect a 

 branch of the bronchus and follow it as far as possible into 

 the lung. 



Exercise 24. Make a drawing of the ventral surface of the lungs, the 

 bronchi, and the trachea with the larynx ; also of the opened larynx 

 from the dorsal side. 



The Nervous System. This system is composed of ( i ) the cen- 

 tral nervous system, or the brain and spinal cord ; ( 2 ) the periph- 

 eral nervous system, which is composed (a) of the paired cranial 

 and spinal nerves and (b) of the sympathetic nervous system; and 

 (3) the special sense organs. 



We shall first study the spinal nerves and the sympathetic 

 system. 



