THE LARYNX. 451 



the opposite plate, a receding angle occupied by the crico-thyroid membrane ; 

 the posterior gives attachment to the crico-thyroid muscle. The extremities 

 constitute the acute angles of the thyroid plate. The anterior is confounded 

 with 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, which articulates with the concave facets of the external 

 face of the cricoid cartilage. 



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



EPIGLOTTIS. This piece forms a soft and flexible appendix, 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 two faces, two 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-epiglottidean 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 tirytenoid cartilage by 

 means 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 aryteno-epiglottidean fold of mucous 

 membrane which extends from the apex of the arytenoid cartilage to the side of 

 the epiglottis.) The base is thick, and articulated with the middle part of 

 the thyroid ; it gives origin, posteriorly, to two lateral prolongations, which 

 pass to the inferior border of the arytenoids, but usually without joining 

 these. 



The summit unites the iree portion of both borders, and is thrown forwards 

 on the upper face of the soft palate (Fig. 174, 9). 



ARYTENOID CARTILAGES. Tkese two pieces have been so designated from 

 their resemblance, when approximated, to the mouth of a pitcher (dpvrau/a, 

 et8os, like a pitcher). They are situated in front of the cricoid, 

 above the entrance to the larynx; each affects an irregular quadrilateral 

 form, and presents for study two faces and four borders. The internal face 

 is smooth, almost flat, and lined by the laryngeal mucous membrane. 

 The external face is divided by a ridge into two portions : a superior, covered 

 by the arytenoid muscle ; and an inferior, giving attachment to the thyro- 

 arytenoid and lateral crico-arytenoid muscles. The superior border is concave, 

 and joined to that of the opposite cartilage. The inferior border gives 

 attachment, posteriorly, to the vocal cord. The anterior border, thick and 

 convex, and covered by the mucous membrane, circumscribes, superiorly 

 and laterally, the entrance to the larynx : it is in joining above, with the 

 homologous border of the other arytenoid cartilage, that the pitcher- beak 

 already mentioned is formed. The posterior border projects into the larynx 

 by its inferior portion ; superiorly, this border is very thick, and is hollowed 

 by a small articular facet, which responds to the anterior facet of the bezel 

 of the cricoid. Above, and to the outside of this facet, is a very prominent 

 tubercle which terminates behind the crest of the external face, and gives 

 attachment to the posterior crico-arytenoid muscle. 



ARTICULATIONS OF THE LARYNGEAL CARTILAGES (Figs. 227, 228), These 

 articulations are of the simplest kind. They are as follows : 



A. The thyroid cartilage is joined to the os hyoides : ], At the 



