AQUATIC MAMMALS 



I have for hours watched the breathing actions of various pinnipeds. 

 By far the greater part of the time phocids inhale rapidly and then 

 close the nostrils, although occasionally they are kept open for the dura- 

 tion of several breaths, especially when the animal comes to the surface 

 after a period of active swimming. And a definite impression is given 

 that the closed position is the relaxed one. In the sea-lions the mecha- 

 nism for involuntary closure seems to be less perfected, but the mystaceal 

 pads are not so broad, the animal is more prone to maintain the nostrils 

 open between breaths (and, incidentally, to breathe through its mouth), 

 and one is unable to decide from observation whether the opened or 

 closed position is the involuntary one. Similarly with the otter. Al- 

 though the muzzle of the latter appears very broad this is partly at- 

 tributable to the rostral breadth of the skull and the pads are really 

 not as large as they seem. 



I have been unable to tell by observation of both American and 

 Asiatic tapirs just how the nasal passages are closed. Apparently there 

 is a contraction of the proboscis and consequent crowding of parts of 

 the passages deep to the apertures. In this group of mammals there 

 are diverticula of the nasal passages comparable to those existing in the 

 Equidae, but no use is known for them. 



In the Hippopotamidae the nostrils take the form of a pair of slits, 

 closure seems to be partly voluntary, and opening accomplished by 

 muscular pull along both borders of the slits. 



I have been unable to acquaint myself with the exact processes of 

 narial action in the Sirenia. The apertures are each somewhat crescentric 

 and closure is evidently chiefly involuntary and largely of the valvular 

 type, like a modification of the condition in the Odontoceti. The nostrils 

 are located at the angle of the muzzle and are evidently farther back in 

 the dugong than the manati. Their present position may be perfectly 

 ideal for the needs of these sluggish creatures and it is by no means 

 certain that there is any stimulus whatever for further migration of the 

 nostrils toward the rear. The extensive rostral basining in this order 

 indicates a high development of the naso-labial musculature, but from 

 Murie's (1872) descriptions I judge that this concerns chiefly the lip 

 movements. The muscular complexity which exists in this region 

 may well be an inheritance from proboscidean ancestry more properly 

 than a relatively recent specialization in response to generic needs. 



For a proper understanding of the narial equipment in the Cetacea it 

 will be necessary to consider the lungs and progress therefrom anterior- 

 ward. Wislocki (1929) has announced that in the porpoise Tursiops 



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