1446 THE VOICE. [BOOK in. 



passages and the mouth, as well as to a certain extent the larynx 

 below the glottis, the trachea and the lungs. 



900. The framework of the larynx consists chiefly of two 

 cartilages, the thyroid and the cricoid cartilages. 



The cricoid cartilage (Fig. 181 Gri.) is, practically, a largely 

 developed tracheal ring ( 319). Forming a complete thick hoop, 

 high behind and low in front, the upper edge sloping downwards, 

 it is attached all round by membrane to the tracheal ring below, 

 and may be regarded as moving upon that ring as well as moving 

 with the rest of the trachea. 



The thyroid cartilage (Fig. 181 Th.) is also a hoop of cartilage 

 but is largely open behind so as to present in horizontal section 

 the figure of a horse-shoe (Fig. 188), is larger in its vertical 

 dimensions than is the cricoid, and is of peculiar form, both its 

 upper and lower border ending behind in the form of a horn, the 

 superior and the inferior cornu (Fig. 181 c.s., c.i.}. The end of each 

 lower horn is definitely articulated to a portion of the hinder 

 lateral surface of the cricoid ; but otherwise the attachments of 

 the two cartilages are membranous only, so that the thyroid can 

 to a certain extent move downwards and forwards upon the cricoid 

 or the cricoid, especially in its front part, can be pulled up towards 

 the thyroid. 



The thyroid cartilage is connected with the hyoid bone above 

 partly by muscles but especially by the thyro-hyoid membrane, 

 which stretches from the upper border of the thyroid along its 

 whole length to the lower border of the hyoid, and the hind edges 

 of which, passing from the ends of the upper cornua of the thyroid 

 to the ends of the great cornua of the hyoid, are strengthened by 

 elastic tissue into rounded cords, the lateral thyro-hyoid ligaments. 

 This membrane permits the whole larynx to be drawn up within 

 the sweep of the hyoid bone. 



Placed behind the thyro- hyoid membrane and imbedded in the 

 mucous membrane lining the pharynx and upper part of the 

 larynx is the rhomboidal plate of yellow elastic cartilage which 

 forms the body of the epiglottis. The greater part of the epi- 

 glottis projects into the cavity of the pharynx as a tongue- 

 shaped process (Figs. 182, 183) presenting an anterior and posterior 

 surface and placed generally at an angle of about 45 with the 

 horizon ; in children it is often more erect and in adults is 

 sometimes more horizontal. The base forms part of the margin 

 of an aperture which we shall presently speak of as the " superior 

 aperture of the larynx" and which at times, as in swallowing, 

 is covered over and so closed by the folding back of the free 

 epiglottis. 



901. Seated on the upper border of the back part of the 

 cricoid on each side of and at some little distance from the middle 

 line are two smaller cartilages deserving especial attention, the 

 arytenoid cartilages (Fig. 181 Ary.~). 



