684 



MAMMALIA. 



Fig. 317. 



poured through the vena cavte into the right or pulmonic auricle ; 

 and hence it passes into the right ventricle (Jig. 317, b), to be 

 again returned through the pulmonary artery to the lungs, thus 

 completing the circulation. 



(780.) But although the general arrangement of the circulatory 

 and respiratory organs in all Mammals thus in every respect re- 

 sembles that which exists in the human body, there are of ne- 

 cessity variations in the distribution of certain parts of the san- 

 guiferous system, adapted to the peculiarities of organization pre- 

 sented by the different orders and even families of this great class, 

 which must not be wholly passed over in silence. 



(781.) In the GET ACE A, for instance, many interesting circum- 

 stances are observable in 

 the arrangement of the 

 vascular system. 



In the herbivorous ge- 

 nera, as for example in 

 the Dugong, the two 

 sides of the heart are 

 separated to a consider- 

 able extent by a deep 

 fissure (Jig. 317, cr, &), 

 so that the pulmonary 

 and systemic hearts are 

 much more evidently dis- 

 tinct viscera than they ap- 

 pear to be in the quadru- 

 pedal forms ; neverthe- 

 less, in the Whalebone and Spermaceti Whales the heart assumes 

 the usual appearance, and is only remarkable for its amazing size ; 

 this, indeed, may well have attracted the notice of Hunter,* while 

 investigating such gigantic beings. " In our examination of par- 

 ticular parts," says that eminent anatomist, " the size of which is 

 generally regulated by that of the whole animal, if we have only 

 been accustomed to see them in those which are small or middle- 

 sized, we behold them with astonishment in animals so far exceed- 

 ing the common bulk as the Whale. Thus the heart and aorta 

 of the Spermaceti Whale appeared prodigious, being too large to 

 be contained in a wide tub, the aorta measuring a foot in diameter. 



* The Animal (Economy, by J. Hunter, with Notes by Professor Owen, p. 366. 



a 



