THE LARYNX. 529 



ference, comprised laterally ber,\veeii the two branches of the thyi'oid cartilage, is 

 concave in the narrow part opposite tlie bezel, where it shows two lateral convex 

 articular facets for articulation with the arytenoid cartilages. The infprior cir- 

 cumfcreme is related to the first ring of the trachea ; it has a small notch, often 

 double, on the middle of the bezel. 



Thyroid Cartilage (Rupee's, cT^os, "like a shield") (Fig. 311, t).— This is 

 composed of two lateral plates, which have the form of an obliquangular parallelo- 

 gram, and are united at their anterior extremity to form a thick constricted part 

 which, in Veterinary Anatomy, is named the body of tfw thyroid. This bodij is 

 smooth on its inferior fare, where it is covered by the terminal extremities of the 

 subscapulo-hyoideii muscles. On its superior fare is an obtuse, rounded, and 

 irregular protuberance, on which the epiglottis articulates. 



The plates, lateral branches, or aloi of the thyroid, present tivo faces, two 

 ■borders, and two extremities. The externcd face, slightly convex, is covered l)y 

 the hyo-thyroideus and thyro-pharyngeus muscles. The internal fare, slightly 

 concave, is covered, near the superior border, by the pharyngeal mucous mem- 

 brane ; for the remainder of its extent it is in contact with the thyro-aryta^noid 

 and lateral crico-arytaenoid muscles. 



The superior border is divided by a small prolongation into two parts — an 

 anterior, giving attachment to the thyro-hyoid membrane ; the other posterior, 

 into which is inserted the palato-pharyngeus muscle. This appendix — the greed 

 thyroid cornu of Man — forms one of the obtuse angles of the parallelogram repre- 

 sented by each lateral plate of the thyroid cartilage ; it is united to the extremity 

 of the hyoid cornu ; and at its base is an opening, or deep notch, through which 

 passes the superior laryngeal nerve. The inferior border is also divided into two 

 parts by the second obtuse angle of the cartilage : the anterior part forms, with 

 that of the opposite plate, a receding angle occupied by the crico-thyroid mem- 

 brane (Ugamentum crico-thyroideum medium) ; the posterior gives attachment to 

 the crico-thyroid muscle. The extremities constitute the acute angles of the 

 thyroid plate. The anterior joins that of the opposite branch, to form the body 

 of the cartilage. The posterior, slightly curved downwards, is terminated by a 

 small, convex, diarthrodial facet, w^hich articulates with the concave facets on the 

 external face of the cricoid cartilage. 



The thyroid cartilage is frequently partially, or even entirely, ossified. 



Epiglottis (Fig. 'd\\, e). — This is a soft and flexible apiiendage, shaped like 

 a sage-leaf ; inferiorly, it circumscribes the entrance to the larynx, and is bent 

 over it, so as to close it hermetically when the alimentary bolus is traversing the 

 pharyngeal vestibule. 



This cartilage has tivo faces, tivo lateral borders, a base, and a summit. The 

 anterior face is convex from side to side, concave from above to below, and covered 

 by the mucous membrane of the pharynx : it gives attachment to the hyo-epiglot- 

 tidean muscle. 



The posterior face shows an inverse configuration, and is covered by the lining 

 membrane of the larynx, which is perforated by glandular orifices. The borders 

 offer a free portion, which aids in circumscribing the entrance to the larynx ; 

 as well as an adherent part fixed to the arytaenoid cartilage by meaiis of a mucous 

 fold, and made irregular by the little cartilaginous bodies which are superadded 

 to it. (These are the cuneiform cartilages, or cartilages of Wrisberg, placed in the 

 aryt^eno-epiglottidean fold of mucous membrane, which extends from the apex of 

 the arytaenoid cartilage to the side of the epiglottis.) The base is thick, and 



