232 THE ANATOMY OF THE HORSE. 



The epiglottis is superposed to it, the two cartilages being united by 

 elastic fibres. On each side it is continuous with the wings. Each ala 

 is a rhomboidal plate of cartilage. The outer surface is slightly convex, 

 and the inner is correspondingly concave. The upper edge of the cartilage 

 is attached to the thyroid cornu of the hyoid bone by the thyro hyoid 

 membrane. The lower edge slightly overhangs the cricoid, and receives 

 the insertion of the crico-thyroid muscle. The other two edges are 

 directed obliquely, one backwards and upwards, the other forwards and 

 downwards. The first of these receives the insertion of the palato- 

 pharyngeus muscle ; the other, in receding from the corresponding edge 

 of the opposite wing, leaves beneath the body a triangular gap which is 

 occupied by the crico-thyroid membrane. Of the four angles of each 

 plate, three demand mention. The supero-anterior angle is acute, and 

 joins the ala to the body of the thyroid. The supero-posterior angle is 

 obtuse, and carries a small bar of cartilage — the superior cornu of man — 

 which is articulated to the extremity of the thyroid cornu of the hyoid 

 bone. Close to the base of this process the plate is perforated by a 

 foramen for the passage of the superior laryngeal nerve. The postero- 

 inferior angle is acute like the first, to which it is diagonally opposite- 

 It is drawn out a little, forming a projection — the inferior cornu of 

 man — which is terminated by a convex facet for articulation with the 

 cricoid. The thyroid is composed of hyaline cartilage. 



The Arytenoid Cartilages. These stand at the upper aperture of 

 the larynx like the mouth of a pitcher, and from this resemblance they 

 are named. They are irregular in shape, but each bears some resemblance 

 to a three-sided pyramid. The inner surface of the pyramid is covered 

 by laryngeal mucous membrane ; the outer surface receives the insertion 

 of the thyro-arytenoid muscle ; the posterior surface is covered by the 

 arytenoid muscle. The base of the cartilage possesses within its area a 

 smooth, depressed facet for articulation with the cricoid. Two of the 

 angles of the base require particular notice, viz., the anterior angle, which 

 is pointed and projects horizontally forwards to receive the insertion of the 

 vocal cord ; and the postero-external angle, which is thick and rounded, 

 and receives the insertion of the crico-arytenoid muscles. The apex is 

 directed upwards, and is prolonged by a slender piece of yellow fibro- 

 cartilage representing the corniculum laryngis of man. This curves back- 

 wards and imvards ; and with the corresponding process of the opposite 

 side forms, behind the upper aperture of the larynx, the pitcher-like lip. 

 Except in the apical prolongation, which is composed of yellow or elastic 

 fibro cartilage, the texture of the arytenoid is hyaline cartilage. 



The Epiglottis is shaped like an ovate, pointed leaf. Its anterior 

 surface is concave in the vertical direction, and convex from side to side. 

 Near the base it receives on the middle line the insertion of the hyo- 

 epiglottideus muscle. The posterior surface has the converse configura- 



