136 EQUINE ANATOMY. 



Insertion. Posterior border of thyroid. 



Action. Brings two cartilages together. 



Posterior crico-arytenoid. 



Origin. Posterior flattened part of cricoid. 



Insertion. Posterior tubercle of arytenoid. 



Action. Rotates the arytenoids outward, thus separating vocal 

 cords. 



Lateral crico-arytenoid. 



Origin. Anterior border of side of cricoid. 



Insertion. Outside the preceding on tubercle of arytenoid. 



Action. Antagonist to preceding, approximating cords. 



Thyro-arytenoid. 



Origin. By two fasciculi, near angle of thyroid. 



Insertion. Lies on vocal cord, to external crest of arytenoid 

 and muscles. 



Action. Constrictor and regulator of tension of larynx. 



Arytenoid. 



Origin. From external face of one cartilage. 



Insertion. Into the analogous point of the other. 



Action. Brings vocal cords in apposition. 



Mucous Membrane. 



Covered by flattened epithelium on cords and glottis; else- 

 where is ciliated. 



The glands are racemose and numerous posteriorly. 



Vessels. 



Laryngeal arteries. 



Nerves. 



Superior laryngeal supplies mucous membrane with sensation 

 and crico-thyroid muscle. The inferior laryngeal supplies the 

 remainder. 



In the mule and ass there exists a deep depression, the sub- 

 epiglottic sinus, capable of great vibration. 



TRACHEA. 



This is a long tube composed of about fifty cartilaginous rings, 

 beginning at the cricoid and ending at the right side of the pos- 

 terior aorta opposite the left auricle of the heart. It lies under 

 the oesophagus and between the two carotids in the' neck. At its 

 end it bifurcates into the two bronchi. 



