803 



MAMMALIA. 



To smell in water would require the nose of a fish, which could not be 

 granted without infringing upon the laws that regulate the progression 

 of animal organization. To smell in air would be useless to the Whale ; 

 and moreover its nasal passages are required for another function, with 

 which the exercise of smell would apparently be incompatible. 



(2365.) Thus circumstanced, we find the whole nasal apparatus com- 

 pletely metamorphosed, and so disposed as to answer two important 

 purposes: viz. first, to allow the Cetacean to breathe air whilst its 

 mouth is immersed in water ; and second, to provide an outlet whereby 

 the water that is necessarily taken into the mouth may escape without 

 being swallowed. 



(2366.) The arrangement adopted to attain both these ends is very 

 beautiful. The nostrils, instead of occupying their usual position, are 

 situated quite upon the top of the head (fig. 407, a) ; so that as soon as 

 the vertex reaches the surface, air is freely obtained. But another 

 difficulty remains to be overcome : how is the Cetacean to breathe air 

 while its mouth is full of water ? 



(2367.) To allow this, the upper extremity of the larynx is prolonged 

 so as to form a thick cartilaginous plug (c). When the creature breathes, 

 this elongated larynx is introduced into the posterior nares, as repre- 

 sented in the figure ; and, being firmly embraced by a sphincter muscle 

 whilst in that situation, the air is admitted into the trachea through the 

 passages (a, 6), without ever entering the oral cavity. 



Fig. 407. 



Blowing apparatus of the Porpoise. 



(2368.) It only remains to be seen how the Cetacean gets rid of the 

 water taken into the mouth, without being obliged to swallow it ; and 

 the same figure, representing a vertical section of the head of a Porpoise, 

 will enable us to understand the mechanism whereby this is accom- 



