DISTRIBUTION OF BLOOD-VESSELS. 259 



loris, which resemble the sloth in the extreme slug- 

 gishness of their movements. It is extremely pro- 

 bable, therefore, that this peculiarity in the mus- 

 cular power results from this remarkable structure 

 in the arteries ; or is at least in some way connected 

 with it. In the Lion, and some other beasts of 

 prey, a similar construction is adopted in the arteries 

 of the head ; probably with a view to confer a power 

 of more permanent contraction in the muscles of 

 the jaws for holding a strong animal, such as a 

 buffalo, and carrying it to a distance. 



In the Cetacea a remarkable provision has been 

 made for affording to the system a sufficient supply 

 of arterial blood during the occasional suspension 

 of respiration which occurs while they dive into the 

 deep recesses of the ocean. The intercostal arteries, 

 which are sent off from the aorta to the spaces be- 

 tween the ribs on each side, are, in these animals, 

 enormously dilated, and contorted into thousands 

 of convolutions, united by a very elastic cellular 

 tissue, and form an accumulation (or plexus) of 

 vessels, of great bulk, which extends along both 

 sides of the vertebral column, and back of the 

 chest. These vessels are thus capable of retaining, 

 as in a reservoir, a very large quantity of blood 

 which has been arterialised, and which may be 

 available, for a certain time, to the purposes of the 

 circulation, during the temporary privation of 

 atmospheric air.* 



* This curious structure was first noticed in the whale, by Hunter, 

 (Phil. Trans, for 1787); and has since been minutely described in 

 other cetacea by Breschet. (Histoire Anatomique et PhysiolDgique 

 d'un organe de nature vasculaire decouvert dans les Cetaces, &c., 

 Paris, 1838.) 



