AQUATIC MAMMALS 



lungs is shifted by just so much toward the center of the body. In 

 such a mammal as man the lungs tend to raise the anterior portion of 

 the body, while there is a corresponding depression of the posterior end, 

 in the water. This is not as yet entirely overcome in the pinnipeds, 

 but in sirenians and cetaceans the natural position by flotation is hori- 

 zontal, largely permitted by the alteration of the diaphragm and lungs. 



VASCULAR SYSTEM 



There are many points of interest connected with the vascular system 

 of certain aquatic mammals, but it is as yet uncertain just what applica- 

 tion these may have to life in the water. It is known that pinnipeds 

 and cetaceans are abundantly supplied with blood. The accounts of 

 sealers frequently make reference to this fact. Whether this character 

 is more pronounced in the Pinnipedia is unknown, but it may well be 

 so, for several authors, notably Murie, have shown that the seal, sea- 

 lion and walrus are equipped with a capacious dilation of the vena cava 

 in juxtaposition with the liver, absent in the Cetacea. I have verified 

 this particular for the seal and sea-lion, and have found that in a young 

 individual of the latter it was notably less marked, which seems to indi- 

 cate that it is an ontological development. The capacity of this hepatic 

 sinus is quite astounding and, as Murie has remarked, it would seem 

 to occupy as much space when expanded as the liver itself. It cannot 

 be doubted that it functions as a blood reservoir. 



The cetacean heart is noteworthy in many respects as enumerated in 

 the literature. Apparently it is larger than in a terrestrial mammal of 

 equal mass, for G. B. Wislocki tells me that the heart of a Tursiops, 

 weighing perhaps 600 pounds, is larger than that of an ox. Owen noted 

 that the heart of a large whale may be more than a yard broad and not 

 much less in length. The axis of the heart has also shifted, with apex 

 more dorsal than in other mammals. The papillary muscles are usually 

 said to be enormous and the organ of such conformation as to indicate 

 great potential power. 



Kiikenthal (1922), quoting various sources, has remarked the strong 

 enlargement of the spinal meningeal arteries within the vertebral canals 

 of the Cetacea. He considered that by this provision the blood supply 

 of the brain escapes the effect of great pressure when the animal dives 

 deeply. This attitude is scarcely justified, however, for it is hardly pos- 

 sible that during long submergence the pressure of the blood could be 

 much less in one part of the body than another. But something of im- 

 portance seems indicated, for Kiikenthal stated that in baleen whales 



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