RESPIRATION IX THE CHELONIA. 21 



The latest and best work on comparative anatomy and physiology 1 thus 

 describes its author's conclusions as to this subject: "C'est aussi par dcs mouve- 

 ments de deglutition que la majeure partie de l'air inspire* est pousscc dans les 

 poumons chez les tortues; mais ici ce mode de respiration est necessity par une 

 disposition organique inverse de eelle queje viens de signaler chez les Batraciens." 

 M. Edwards then proceeds to point out the rigid form of the turtle's frame, the 

 absence of mobile ribs, and the consequent necessity for the belief that the lungs 

 in these animals cannot be dilated from without, as occurs in mammals. The same 

 opinion is held by nearly all writers at the present time ; but some, in place of 

 describing the process as one of deglutition, effected alone by muscles on the floor 

 of the mouth, regard the hyoid apparatus as the true forcing pump concerned in 

 propelling air into the interior. Thus, T. Rymer Jones, 2 after describing the 

 fixity of the bones of the chest in turtles, adds, that "under these circumstances, as 

 a compensation for the want of mobility in the chest, the os hyoides and the mus- 

 cles of the throat arc converted into a kind of bellows, by which the air is forced 

 mechanically into the lungs, and they are thus distended at pleasure." In fact, the 

 submaxillary space with the hyoid arches, are in continual motion in turtles, and this 

 movement precisely resembles the like action in frogs; but while in these latter it is 

 really a respiratory act, in turtles, as we shall show, it has other purposes, and, while 

 it has deceived observers, may be proved to have no influence of any moment in 

 carrying on the breathing process. Midler 3 gives a like account, and adds, that 

 expiration is effected by means of muscles between the lower shield or plastron, 

 and the posterior extremities. Carpenter 4 has a brief description of the respiration 

 in chelonia, which corresponds to the general opinion already quoted above. 



Prof. Agassiz's description 5 being one of the latest, and certainly one of the most 

 authoritative statements, we quote in full, to complete our history of the generally 

 received ideas as to the mechanism of chelonian respiration. 



" Here, again, we meet with a very striking ordinal character. The turtles 

 swallow the air they breathe. The breast box, which includes the lungs, being 

 immovable, a respiration like that of the other reptiles, the birds, and mammalia, 

 performed by the expansion and compression of the breast box, and consequently 

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

 ing is therefore only possible for turtles, by a pressure 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 the opinion of other anatomists, 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 the shoulder and of the pelvic region may assist in that 



1 Milne Edwards, Lecons sur la Physiologic et l'Anatomie coinparec de I'Homme et des Animaux, 



deuxieme, deuxiemc partie, p. 387. 1S58. Paris. 



The General Structure of the Animal Kingdom, p. 5G7. 



3 Physiology — London translation, p. 360, vol. ii. 



4 Gen. and Com]). Phys., p. 493. 



■ Contributions to the Natural History of the United Stales, vol. i. p. 281. 



