Chap. I. 



RESPIRATION. 



281 



SECTION XI, 



RESriKATION. 



Here, again, we meet Avith a very striking ordinal character. The Turtles 

 swalloAV tlie air thc}^ breathe.^ The breast-box, which includes the lungs, being 

 imTnoval)le, a respiration lilce that of the other Reptiles, the Birds, and Mammalia, 

 performed by the expansion and compi'ession of the breast-box, and consequently 

 of the lungs, is impossible. Owing to the peculiar structure of their trunk, Ijreath- 

 ing is, therefore, oidy possible for Turtles by a pressui'e of the air from the 

 mouth down into the lungs; but, though we are persuaded that this swallowing 

 of the air constitutes the main act in the process of breathing, still we are inclined 

 to believe, against tlie opinion of otlier ajiatomists, that the diaphragm, which in 

 Turtles is very much developed, and attached to the lungs, takes also its part 

 in that act.^ Moreover, the muscles of tlie shoulder and of the 2)elvic region may 

 assist in that operation, either I)y immediately compressing the lungs, which generally 

 extend in Turtles from one end of the trunlc to the other, or by pressing the 

 bowels against tliem. 



The act of swallowing the air is chiefly jierformed by the apparatus of the 

 tongue-bone, and the tongue itself, Avhich, hy its large size, facilitates the opera- 

 tion. Being <lraAvn liackAvards and upwards, this organ shuts uyi the choanna?, and 

 at the same time opens the slit of the windpipe, situated just at its base, thus 

 giving to the air a passage into the windpipe, and at the same time preventing 

 its entrance through the choannte into the nose. In this wa}", the tongue takes the 

 place, in a certain sense, of the velum palatinum of the higher Vertebrata, which 

 is wanting in Tvu-tles. After the air has passed into the windpipe, the tongue is 

 drawn forwards, and thus the longitudinal glottis is again closed, Avliile now the 

 choaima} are again opened to a free comuuniication with the cavity of the month.^ 



* ^Vc fiml the same moilo of l)rnatliinjr in flie 

 class of Uatrachians ; Imt for an cntiirly ditlcrcnt 

 reason, namely, on account of the ah.<(;ncc of ribs. 



* The existence of a diaphragm is erroneously 

 denied to Turtles hy Dumeril and Bihron, Erpe- 

 tolojiie frenerale, I., ]>. 17-'). This work, however, 

 worked out as it seems almost entirely hy 15ihron, 

 is to this day the I)cst illustration of the Zoiilogy 

 of Turtles, as it also is of the Saurians and Frogs, 



36 



while the part relating to Ophidians, completed after 

 the early deatli nf that able Iierpetologist, Bibron, 

 contains the most superficial descriptions of genera 

 and species. 



' In Amphibia, this process is similar, though not 

 the same. It is easy to observe, lliat iti this class 

 the eye-biilbus is often active in swallowing the 

 air; these large balls, when pressing downwards, 

 narrow tlic cavity of the mouth, and tlie air moves 



