WARM-BLOODED CIRCULATION. 



279 



all united in one envelope, so as to compose 

 in 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 



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 

 systemic auricle, e the right or 

 pulmonary ventricle, f the pul- 

 monary artery, k the left or 

 pulmonary auricle, l the left 

 or systemic ventricle, and a the aorta. 



