.,., a N A T M V A N 1) P H YSIO 1. (1 V P 



ttion, either by immediatelj compressing the inn--, which generally extend in 



turtles from one end of the trunk to the other, or by pi the bowels against 



them. 



"The art of swallowing the air is chiefly performed by the apparatus of the 

 tongue-bone, and the tongue itself, which, by its large size, facilitates the operation. 

 a drawrj backwards and upwards, tin- organ shuts up the choann®, 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 choannse into the nose. In this way. the tongue takes the place, in a 

 certain sense, of the velum palatinum of the higher vertebrata, which is wanting 

 in turtles. After the air has passed into the windpipe, the tongue is drawn for- 

 wards, and thus the longitudinal glottis is again closed, while now the choannse are 

 again opened to a free communication with the cavity of the mouth." 



Professor Agassi/, adds, in a following note: — 



■•We find the same mode of breathing in the class of Batrachians, but for an 

 entirely different reason, namely, on account of the absence of ribs." 



Also. "The existence of a diaphragm is erroneously denied to turtles by 

 Dumeril and Bibron, Erpetologie generate, 1, p. 17")." 



In the above description, Prof. Agassiz exhibits some doubt, as to the correctness 

 of received views on this subject, and speaks of the museums diaphragmaticus 

 (Bojamis) as having something to do with the act of respiration, which he thinks 

 may also be aided by other muscular parts, as those concerned in Locomotion, and 

 bv certain pelvic muscles which lie does not specify by name. 



We shall show as we proceed that, although the muscle covering the lungs maj 

 be homologous with the diaphragm of mammals, it is really a muscle of expiration, 

 and therefore not analogous to the diaphragm when regarded from a physiological 

 stand-point. 



Except for the purpose of completing this brief history of opinions held now or 

 abandoned, it is only requisite to allude to the views of Perault, who attributed the 

 inspiratory act to the elasticity of the lungs, and the expiratory motion to muscles 

 of which, he says naively, the turtle has an abundance. M. Tauvry, whose views 

 Milne Edwards partially indorses, attributed the whole respiratory act to the 

 changes in the capacity of the chest, caused during locomotion, by the advance of 

 the head and limbs from and their retraction within the carapace. ML. Ilaro' sup- 

 ports the same views, but, although both are successful in showing that these 

 movements may alter the capacity of the chest-box, and thus under some circum- 

 stances modify respiration, neither has proved that respiration relies for its continued 

 occurrence upon these motions, nor would such a supposition be entertained for a 

 moment by any one who surveyed the mechanical conditions which are effective in 

 carrying on respiration in other animals. That the locomotive movements may, and 

 p ill aps do at times modify the respiratory process, may be taken for granted. That 

 other agents are constantly employed in this function is not less clear, nor shall we 

 have any difficulty in disproving M. Haro's theory bj unanswerable facts. 



1 Mem. sur le respiration des Grenouilles, Ann. des Si-. Nat. -J serie, t. xviii. p is 



