R B S I' 1 R A T 1 o N I N THE (II E I, X I A. 



bone, in its movements, carries with it (Ik- glottis, and removes it from obstructions 

 during inspiration. The larynx. Fig. '-\ A and B, cousins of a largely-developed 

 cricoid cartilage and two arytenoid cartilages. The cricoid rests in the howl of the 

 hyoid hone, is somewhat helmet-shaped, and has on ils under surface a visor-like oval 

 fenestrum. This fenestrum is covered by membrane, and is traversed from side to side 

 by the chiasm of the superior laryngeal nerves, of which we shall speak more fully 

 hereafter. Superiorly the cricoid presents an oval opening, filled in by membrane, 

 upon which rest the arytenoid cartilages, one on either side, with the glottic slit 



Fig. 2. 



B 



b b'. Cricoid cartilage; c, left arytenoid cartilage; 

 a', cartilaginous tubercle capping the apex of 

 the arytenoid cartilage ; a, oval fenestrum of 

 cricoid, filled in with membrane. 



b. Cricoid cartilage; a, superior opening; c, trachea. 



between them. The arytenoid cartilages, Fig. 2, A, c, are two irregularly triangular 

 solids, opposing fiat surfaces to each other, their bases incorporated with the superior 

 cricoid membrane, and their apices extending vertically, and terminating in a small 

 cartilaginous tubercle. They are the framework upon which the crico-hyoid and 

 crico-arytenoid muscles act, in closing and opening the glottis. The trachea, 

 smaller in diameter than the cricoid bulb, descends the neck, inclining to the left 

 side, until opposite the margin of the shell it divides into two bronchi, which, 

 curving right and left, open free into the corresponding lungs, at the under and 

 inner edge, a little behind the anterior extremity. The lungs are two wedge-shaped 

 sacs, the base of the wedge being anterior. They lie in contact with the vault 

 of the dorsal shield, and are separated from each other by the large retractor mus- 

 cles of the neck, the bloodvessels, and nerves. They are anterior and above the 

 peritoneal sac, except the posterior pointed extremity, which projects into that 

 cavity, carrying with it a covering of peritoneum. The walls of the lungs being 

 elastic lend aid to the act of expiration, but as they give no evidence of muscular 

 fibre to mechanical or galvanic stimuli or to the microscope, it is impossible, for 

 this and for other reasons, to suppose with Varnier that they possess any intrinsic 

 power to assist in the act of inspiration. 



The turtle which has served us for most of our experiments, is Chelydra Ser- 

 pentina, the well-known Snapping Turtle of the United States. Selected at first 

 from the facility with which we could procure fine specimens, we soon found that its 

 well developed muscular system and its exposed flanks admirably fitted it for the 

 study of respiratory myology, while its middle rank among Testudinata led us to 

 expect, in its organization, more striking ordinal characters than we would find in 

 the extreme marine or terrestrial families. We have therefore adopted Chelydra 



2 



