ORGANS OF RESPIRATION. 



rial and other birds, with less power of modulating their 

 sounds, there is but one pair of these inferior laryngeal 

 muscles, and in the gallinaceous and a few other birds, there 

 are no special muscles for the movement of the inferior 

 larynx, distinct from the ordinary muscles of the trachea. 



The superior larynx is still very simple in birds ; it is much 

 more uniform throughout the class than the inferior, and it 

 more nearly approaches to that of reptiles, especially of che- 

 lonia, than to that of mammalia. The large thyroid cartilage 

 forms the anterior part, and the entire base resting on the 

 first tracheal ring, and its two lateral quadrangular pieces, 

 often detached when ossified, have commonly been mistaken 

 for the cricoid cartilages. These three principal constituent 

 parts of the thyroid, remain united through life in swans, 

 pelicans, parrots, ostriches, and some other birds, especially 

 where they retain their primitive cartilaginous condition ; but 

 where they become ossified, the broad pentagonal anterior, 

 and two lateral four-sided pieces, leave greater or less cartila- 

 ginous interspaces between them, which have impeded the 

 identification of the laryngeal elements of birds. The rudi- 

 ments of tracheal rings are generally seen at the base of the 

 large middle anterior piece of the thyroid, indicating the 

 mode of development and separation of the more perfect in- 

 ferior rings. The thyroid pieces are disunited on the median 

 line behind, though generally in contact ; and on dissecting 

 the inner and upper part of the anterior piece, the cartilagi- 

 nous rudiments of the epiglottis, are seen extending upwards 

 and inwards. In the storks and herons, the processus epiglot- 

 ticus rises upwards broad, like that of an agama among the 

 sauria, and is already ossified in these birds, like most of their 

 tracheal and laryngeal parts. In many gallinaceous and 

 other birds, the epiglottis is flat, thin, and flexible, like that 

 of mammalia ; and the most perfect forms of the epiglottis 

 observed by Henle in the birds, were those of sterna, rallus, 

 and larus } where it is detached from the thyroid cartilage, and 

 extends free, flexible, and cartilaginous, into the pharyngeal 

 cavity. 



Between the posterior ends of the thyroid cartilage, in the 

 angular space commonly left behind by the meeting of its 

 edges, is situated the small cricoid cartilage of birds, of a 

 quadrangular, or triangular form, often ossified, tapering 



oo2 



