WARM-BLOODED CIRCULATION. 27,9 



ill appearance but a single organ:* still, how- 

 ever, the right and left cavities are kept per- 

 fectly distinct from one another, and are sepa- 

 rated by thick partitions, allowing of no direct 

 transmission of fluid from the one side to the 

 other. These two hearts may therefore be com- 

 pared to two sets of chambers under the same 

 roof; having each their respective entrances 

 and exits, with a party-wall of separation be- 

 tween them. This junction of the two hearts 

 is conducive to their mutual strength ; for the 

 fibres of each intermix and even co-operate in 

 their actions, and both circulations are carried 

 on at the same time ; that is, both ventricles 

 contract or close at the same instant; and the 

 same applies to the auricles. The blood which 

 has just returned from the body, and that from 

 the lungs, the former by the venae cavae, the 



* A remarkable exception to this general law of consolidation 



occurs in the heart of the Du- 

 gong, represented in Fig. 360, 

 in which it may be seen that 

 the two ventricles, (e and l), are 

 almost entirely detached from 

 each other. In this figure, which 

 is taken from the Philosophical 

 Transactions for 1820, d is the 

 right or systemic auricle ; e the 

 right or pulmonary ventricle ; f 

 the pulmonary artery ; k the left 

 or pulmonary auricle ; l the left 

 or systemic ventricle ; and a the aorta. 



