ORDER CHELONIA. 49 



and is inserted in the peritoneum ; — this one is the contractor 

 of the lungs, or the expirator muscle. The other extends 

 over almost the entire cavity, between the under part of the 

 carapace, and the inside of the sternum, and is inserted on the 

 edges of the carapace above and below. These muscles act 

 alternately. The first, compressing the little lobe of the 

 lungs, expels the air ; the other, stopping this compression, 

 determines the fresh air to come and supply the place of 

 that which has issued forth. Thus, respiration takes place 

 in this genus, as it does in those which have a genuine thorax ; 

 but it is never so complete, that is, the pulmonary cavity is 

 not emptied at each expiration of all the air which it contained. 

 To this cause, doubtless, as also to the direct passage of the 

 blood from one chamber of the ventricle into another, must 

 be attributed the faculty which tortoises possess of living 

 without respiration at the bottom of the water, and even of 

 not perishing for a long time, in the vacuum of a pneumatic 

 machine. Duvernois explains this action somewhat differently. 

 He believes that the muscles above mentioned do not act 

 directly on the lungs, but on the viscera of the abdomen, 

 which thereby compress the lungs. 



Like other vertebrated animals provided with lungs, the 

 tortoises have a trachea and larynx, capable of producing a 

 voice. It is accordingly ascertained that certain species, 

 chiefly the marine, send forth hissings, and utter cries more 

 or less sharp. They are also said to snore in sleeping. 



Anatomists, for a long time, believed that the heart of 

 reptiles had but one ventricle and one auricle. But it is now 

 ascertained that there are two auricles, and in the tortoises a 

 ventricle separated by a fleshy partition, pierced with small 

 holes ; so that in reality there are two auricles and two ven- 

 tricles in this genus. It is known, moreover, that the tor- 

 toises have a third ventricle in the middle. From this heart 

 proceed three arterial trunks, the insertion of which varies 



VOL. IX. E 



