THE CAT 237 



into a pan of water. Do not cut the nerve cord just mentioned. 

 Note the relation of the hyoid apparatus to the larynx. Carefully 

 dissect away the tongue and expose the hyoid. It will be seen to 

 consist of a transverse median bone, the basihyal, and two pairs 

 of horns, or cornua. The anterior cornua are the longer and consist 

 of four bony segments on a side; the posterior cornua are com- 

 posed of a single bone on each side. 



Study the larynx, first removing the muscles from its sides. 

 The glottis, the opening into the larynx from the pharynx, is a 

 triangular slit in the floor of the pharynx, in front of which is the 

 epiglottis. 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 the large plate on the ventral and lateral sides that forms the 

 anterior ring of the larynx. The cricoid is just behind the thyroid ; 

 it forms a complete ring, which is wide dorsally and narrow ven- 

 trally. The arytenoid cartilages are two small trianglar bodies, 

 articulating with the anterior edge of the dorsal side of the cricoid 

 cartilage, in the median line. 



On each side of the glottis, at the base of the epiglottis, is a 

 pair of fleshy ridges, the false vocal cords ; the vibration of these 

 cords is said to produce purring. Just behind these are the true 

 vocal cords. They are a pair of ridges on the inner surface of the 

 larynx, converging from the arytenoid cartilages dorsally to the 

 inner surface of the thyroid cartilage ventrally. 



Exercise 29. Draw a semidiagrammatic sketch of the anterior end of 

 the larynx, showing the false and the true vocal cords, together 

 with the hyoid bones. 



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, the right lung being divided into four lobes and the left 



