LARYNX. 



127 



cricoid, and passes backwards to be inserted into the inferior cornu 

 of the thyroid ; it draws these two cartilages together obliquely. 



Posterior crico-arytenoid,^ arises from the flat surface on the back 

 of the cricoid, and is inserted into the posterior part of the base of 

 the arytenoid ; it draws the arytenoid backwards, and thus tightens 

 the vocal ligaments. (Fig. 110.) 



Lateral crico-arytenoid.^ — Arises from the side of the cricoid, and 

 is inserted into the side of the base of the arytenoid ; it separates 

 the arytenoid, and widens the glottis. 



Thyreo-arytenoidJ^ — 



Fig. 



110. 



Fig. 111. 



Arises from the posterior 

 face, and near the angle 

 of the thyroid, and is in- 

 serted into the anterior 

 surface of the arytenoid, 

 which it draws forwards, 

 and thus relaxes the vocal 

 ligaments. 



Oblique arytenoid.^ — 

 It consists of oblique 

 fibres arising from the 

 tip of one cartilage, and 

 inserted into the top of 

 another. (Fig. 111.) 



Transverse arytenoid.^ — Arises from the side of one cartilage, 

 and is inserted into the side of the other. These last two muscles 

 are often considered as one, and by them the glottis is narrowed. 



Thyreo-epiglottideus. — Consists of a few fibres passing between 

 these two cartilages. 



Aryteno-epiglottideus, are also a few indistinct fibres passing be- 

 tween the cartilages from which it derives its name. These last two 

 draw the epiglottis downwards. 



TRACHEA. 



The trachea is a cylindrical tube, four or five inches in length, 

 reaching from the larynx as low as the third dorsal vertebra, where 

 it divides into the bronchi. It is formed of from sixteen to twenty 

 cartilages, united by ligamentous tissue, which is of an elastic cha- 

 racter. Each ring is about two lines broad and constitutes two- 

 thirds of a circle ; the first ring is the largest, and the last ring is 

 of such a shape as to be adapted to the first rings of the bronchi. 



The posterior third of the trachea is completed by a muscidar 

 structure, whose fibres are transverse, and the contraction of which 

 diminishes its diameter, by which expectoration is facilitated ; it is 

 lined by a mucous membrane continuous with that of the larynx, 

 which is extremely vascular, and covered with numerous follicles. 



