222 RESPIRATORY SYSTEM. 



This cartilage not only constitutes by far the most extensive part 

 of the larynx, but, as its name indicates, incloses and shields from 

 external injury all the others. 



THE CRICOID or ring-like cartilage is placed below the 

 thyroid. In front it appears like part of the trachea ; but it 

 broadens so much behind, that it overlaps the first rnig of the 

 windpipe, somewhat after the form of a helmet. Upon its broad 

 or posterior part are four surfaces of articulation : the two upper 

 receive the hinder extremities of the arytenoid cartilages, the two 

 lower are adapted to the inferior cornua of the thyroid cartilage : 

 they are all furnished with capsular ligaments and synovial mem- 

 branes. Furthermore, it is attached by ligamentous expansions 

 to those parts, and likewise to the first ring of the trachea. 



THE TWO ARYTENOID, or e?<;er-sA«perf cartilages, trian- 

 gular in their figure, lie over the upper and back part of the tra- 

 chea, leaving an aperture between them leading into that canal, 

 denominated, from its proximity to the tongue, the glottis. Their 

 inward parts are everted, and form a triangular prominent border, 

 over which is spread the membrane of the glottis : their outward 

 surfaces are marked by concavities in which are lodged the aryte- 

 noid muscles. Posteriorly, they repose upon the cricoid cartilage, 

 and are connected with them by capsular articulations : in front, 

 they have a membranous connexion with the cartilage next to be 

 noticed. 



THE EPIGLOTTIS, so named from being raised over the 

 glottis, and occasionally covering it like the lid of a pot, is well 

 adapted, from its heart-like shape, to the rz'wa g/o^^/f/?s ; whose 

 margin is completed by two narrow slips of cartilage proceeding 

 from the base of the lid to the arytenoid. By some, these slips of 

 cartilage have been separately considered : but in my opinion im- 

 properly so ; for they are, in reality, nothing more than prolonga- 

 tions or appendices of the epiglottis. The surface of this carti- 

 lage presented to the interior of the larynx is smooth and concave, 

 and covered by an extension of membrane from the glottis ; that 

 part opposed to the tongue is unevenly convex, and is tied to that 

 organ, as well as to the os hyoides, by a doubling of membrane 

 infolding some muscular fibres : to this musculo-membranous 

 ligature, which assists in retaining the cartilage in its elevated 

 position, the name offrccniim epiglottidis is properly given. The 

 fracnum receives co-operation in this function from strong elastic 

 ligaments connecting the base of the epiglottis to the thyroid and 

 arytenoid cartilages. 



If we detach the epiglottis, or raise it forcibly, in order to ob- 

 tain a more complete view of the rima glottidis, the latter will be 

 found to be stretched inlu an oblong quadrilateral figure, whose 



