MOUTH AND NOSE 



as a series of rather triangular blades, set close together, the outer or 

 labial borders being almost vertical, smooth and firm. The formation 

 is of long fibers cemented together. From the ventral tip of each blade 

 obliquely upward and inward to near the median line of the roof of the 

 mouth the softer cementing substance wears or dissolves away, leaving 

 the fibers to form a brush-like inner border to each plate. These diffuse, 

 intermingle with those of adjoining plates, and form an effective ap- 

 paratus for straining from the water and retaining within the mouth 

 the half inch crustaceans which form the favorite item of food. The 

 baleen of some whales, as the California gray (Rhachianectes) is short, 

 coarse, and commercially valueless. In this whale, as well as probably 

 all baleanopterids, the baleen equipment fits into the closed mouth 

 without bending. In the balaenid (as the right and bowhead) whales 

 the plates are of fine texture and may reach a length of more than 12 

 feet (bowhead), the ends folding upon themselves at the bottom of the 

 oral cavity, but because of their excessive elasticity, they at once spring 

 straight when the mouth is opened and pressure upon the blade tips is 

 released. 



We may, because of the present condition in Phocoenoides, follow 

 the probable course of the development of the baleen with some little 

 feeling of assurance. First starting as short epithelial papillae along 

 the maxillary dental arch, they were used in place of the disappearing 

 teeth to hold and retain small active prey. As they increased in length, 

 water could be squirted out between the papillae so as to separate small 

 fish and similar food held within the mouth, and the further transition 

 of the baleen was but a matter of the ability properly to respond to the 

 stimulus provided, and of sufficient time. The degree to which the 

 baleen has developed in the large balaenid whales surely constitutes an 

 overspecialization at the present time. 



Probably the first modification which an aquatic mammal undergoes 

 is the acquisition of the ability to close the nostrils, for any mammal 

 would be decidedly handicapped during under-water activity by having 

 to guard continually against the sudden entry of water into the open 

 nose. As in the case of the ear, there will tend to be a progressive 

 adaptation in this respect, consisting first of closure with difficulty and 

 then with ease, followed by the time when the closed position is the 

 involuntary one and opening is the voluntary. Cetaceans and probably 

 the Sirenians belong in the last category, while pinnipeds, the otters, 

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