AQUATIC MAMMALS 



The interaction of the specialized facial musculature in opening the 

 nostrils of mysticetes has not yet been investigated with sufficient exacti- 

 tude for us to be sure of all the actions involved. Of course the facial 

 musculature is very highly modified, as it must be to control nostrils 

 situated upon the top of the head, but the intricacy is not nearly so great 

 as in that of the odontocetes. There are sufficient good photographs 

 (see fig. 13) of breathing mysticetes to gain an understanding of the 

 external results when the opening mechanism of the nostrils is in opera- 

 tion. In these there is apparent a marked lateral dilation of the outer lips 

 of the nares, and a surprisingly high elevation of the anterior margins 

 an arrangement which evidently operates as an efficient barrier to the 

 entry of water within the respiratory tract while the animal is in loco- 

 motion. There must be definite mechanical provision for this elevation, 

 either in excessive elasticity of the tissue deep to the anterior margins 

 or in wrinkling, and the latter is exactly what we find in the spritzsack, 

 to which theory Schulte also subscribed. 



The latter authority, in his study of Balaenoptera borealis, indicated 

 uncertainty regarding just how the elevation of the anterior narial lip 

 was instigated. From what I could learn from adult finbacks there is 

 no great difficulty in this. The closed nares are suggestive of a V with 

 apex directed forward, and the open nares are each broadly oval, with 

 the long axes almost parallel. It is clearly evident that the pull of 

 superficial muscles converging to the apertures from rostrad and laterad 

 open the nares. The elevation could easily be provided by superficial 

 muscles pulling rostrad upon the anterior and lateral margins while at 

 the same time antagonistic action is supplied by deeper muscles pulling 

 largely caudad, and relatively nonyielding tissue anterior to the narial 

 passages. This seems to be the general principle of the mechanism, 

 although in reality the actions are likely very intricate. 



The narial conditions in the Odontoceti are very different. In all of 

 them the external aperture is single, in all but the sperm whales medial, 

 and almost always it is crescentric in shape, the concave aspect being di- 

 rected anteriorly. The only known exception to the last detail is in 

 Platanista, in which the orifice is said to be in the form of a longitudinal 

 slit, but in exactly what manner this is opened is unknown. Excepting 

 the latter for the time being, narial development of the toothed whales 

 is of two definite sorts that represented by the Kogidae and Physeteri- 

 dae or sperm whales, and all other odontocetes. The latter, as the least 

 intricate, will be discussed first. In perhaps no two distinct sorts is the 

 facial musculature arranged exactly the same, for as the genera diverged 



[96] 



