432 



THE BODY AT WORK 



Its capacity for vibration depends upon the tenseness which 

 is given to it by the pressure of the lymph with which it is 

 distended, and vast numbers of exceedingly slender elastic 

 fibres which traverse it. 



The first cartilage below the thyroid it may be felt with 

 the finger is termed " cricoid " (rcpUov, a ring), from its 

 resemblance to a signet-ring. Narrow in front, its large signet 



Epiglottis 



- Hyoid Bone 



- Ventricle 



-False Vocal Card 



- T/tyoarytenoid Muscle 



Vocal Cord 



Thyroid Cartilage 



FIG. 44. THE ANTERIOR HALF OP THE LARYNX SEEN FROM BEHIND. 



The drawing shows the folds of mucous membrane, the vocal cords, which stretch from the 

 tips of the arytenoid cartilages to the recess behind the median portion of the thyroid 

 cartilage. To the outer side of each vocal cord is seen the thyro-arytenoid muscle (cut 

 across), consisting of a broad outer portion, chiefly concerned in closing the glottis during 

 the act of swallowing, and a smaller internal portion, which regulates the length and the 

 thickness of the segment of the cord allowed to vibrate. 



projects upwards, within the V of the thyroid, behind, and on 

 the top of the signet rest the two arytenoids. Each arytenoid 

 is a triangular pyramid, its anterior, external, and upper angles 

 prolonged into processes. It is united with the cricoid by a 

 swivel joint, which allows its anterior process to swing inwards 

 or outwards under the influence of two antagonistic muscles 

 attached to its outer angle the lateral and posterior crico- 

 arytenoids. Another muscle attached only to the arytenoids 

 draws them together. Still another muscle or two muscles, 



