THE RESPIRATORY SYSTEM. 169 



end of the trachea, at the base of the tongue. The basi- 

 hyal bone is attached to the cephalic ventral margin of 

 the larynx and on each side is a thyrohyal bone (Fig. 20). 

 Dorsal to the larynx is the esophagus. By removing 

 carefully the muscles and fibrous tissue from the cartilage 

 the larynx is seen to be composed of five pieces: the 

 epiglottis, thyroid cartilage, two arytenoid cartilages, and 

 the cricoid cartilage (Fig. 20). The epiglottis is the 

 small triangular cartilage that closes the glottis when 

 food passes into the esophagus (Fig. 55). The thyroid 

 cartilage constitutes the largest part of the larynx. In 

 man it forms the prominence known as Adam's apple. 

 Dorsally the two halves of the thyroid cartilage are 

 separated, each projecting cephalad into a process known 

 as a cornu. The arytenoid cartilages are the two small 

 paired pieces caudad to the thyroid, on the dorsal side. 

 The cricoid cartilage forms a complete ring at the caudal 

 end of the larynx (Fig. 20). 



There are a number of ligaments connecting the various 

 parts of the larynx, the most important of which are the 

 vocal cords. These are of two kinds true and false. 

 They are best demonstrated by dividing the larynx 

 sagittally. The superior or false vocal cords are the two 

 superior thyro-arytenoid ligaments passing from the 

 arytenoid to the thyroid cartilage, at the base of the 

 epiglottis. The cat is said to use these cords in purring. 

 The inferior or true vocal cords are the inferior thyro- 

 arytenoid ligaments, consisting, as in man, of a fold of 

 mucous membrane on either side, just caudad to the 

 false vocal cords (Fig. 55). The depression on either side 

 between the true and false vocal cords is the ventricle. 

 By means of the muscles attached to the arytenoid 

 and thyroid cartilages, the tenseness of the vocal cords 

 is regulated, and the various pitches of voice produced. 



