MAMMALIA. 685 



When we consider these as applied to the circulation, and figure 

 to ourselves that probably ten or fifteen gallons of blood are 

 thrown out at one stroke, and moved with an immense velocity 

 through a tube of a foot in diameter, the whole idea fills the mind 

 with wonder." 



(782.) In the arrangement of the blood-vessels of the CETA- 

 CEA many interesting peculiarities are met with.* The general 

 structure of the arteries, indeed, resembles that of other Mam- 

 mals, and where parts are nearly similar their distribution is 

 likewise similar. But these animals have a greater proportion of 

 blood than any others known, and there are many arteries appa- 

 rently intended as reservoirs, wherein a large quantity of arterial 

 blood may accumulate, apparently for important purposes, where 

 vascularity could not be the only object. Thus the intercostal 

 arteries divide into a vast number of branches, which run in a ser- 

 pentine course between the pleura and the ribs, and penetrate 

 the intercostal muscles, everywhere lining the walls of the thorax. 

 These plexiform vessels, moreover, pass in between the ribs near 

 their articulation, and anastomose extensively with each other. 

 The medulla spinalis is likewise surrounded with a net-work of 

 arteries in the same manner, more especially as it comes out from 

 the brain, where a thick substance is formed by their ramifications 

 and convolutions, and these vessels most probably anastomose with 

 those of the thorax. The precise function assigned to this ex- 

 tensive plexus of arteries has not been as yet satisfactorily deter- 

 mined, although it is doubtless a receptacle wherein arterial blood 

 is stored up during the long-continued submersion to which these 

 animals are so frequently subjected. 



(783.) As the GET ACE A have no pelvic extremities, the aorta, 

 instead of bifurcating into iliac arteries, is entirely appropriated to 

 supply the enormous tail beneath which it is continued, enclosed 

 in a canal formed by the roots of the inferior spinous processes 

 of the caudal vertebrae, that are here again developed as in fishes. 



(784.) The venous system in the Cetacean order is equally 

 remarkable for the plexuses formed by it in different parts of the 

 body ; of these the most important communicates with the abdo- 

 minal cava, and is of immense extent. The veins of these crea- 

 tures, moreover, are almost entirely deprived of valves, so that 

 every possible arrangement has been made to delay the course of 

 * Hunter, ut supra, p. 365. 



