218 



ANATOMY OF VERTEBRATES. 



the anterior part of the larynx. It is of an oval or triangular 

 form, according as its superior termination is more or less pointed, 

 and answers to the thyroid cartilage, fig. 73, /. The cricoid car- 

 tilage is represented by three osseous pieces, which are situated at 

 the posterior and inferior part of the upper larynx ; the middle 

 one, fig. 73, g, is of an oblong form, and varies in size, being larger 

 than the lateral ones in the Anatidce, but smaller in the Cantores. 

 The lateral pieces are connected at one extremity with the thyroid 

 piece, and at the other to the middle oblong piece above described, 

 which completes the circle of the laryngeal framework posteriorly : 

 the first two incomplete tracheal rings, ib. g, g, may represent the 

 anterior part of the cricoid. The arytenoid bones, ib. A, rest upon 

 the middle oblong portion of the cricoid, and extend forward, 

 being connected at their outer edge by means of elastic celhilar 

 substance to the thyroid, and attached by their anterior extremities 



00 



upper larynx, Crane, xlviv 



Upper larynx. Crane, xlviv 



to the urohyal by means of two small ligaments : they form, by 

 their inner margins, the rima glottidis or laryngeal fissure. 



This fissure, fig. 51, i, being thus bounded by inflexible rigid 

 substances, is only susceptible of having its lateral diameter varied 

 according to the degrees of separation or approximation to which 

 the arytenoid bones are subject. These different states are pro- 

 duced by appropriate muscles, one pair of which may be regarded 

 as Thgreo-argtenoidei, and the other may be termed Constrictores 

 glottidis. The former, fig. 99, k, h, arise from the sides and posterior 

 surface of the thyroid, and are inserted into the whole length of the 

 inner edge of the arytenoids, which they draw outward, and conse- 

 quently open the laryngeal fissure. The Constrictores glottidis in 

 the Gigantic Crane arise from the middle of the internal or posterior 

 surface of the thyroid, and are inserted into the arytenoids : they 

 close the laryngeal opening with such accuracy as to supersede the 

 necessity of an epiglottis. From the simplicity of the structure 



