THE SENSES 



brane is not at all finger-shaped but is gently bowed and often partly 

 calcified. In the whalebone whales (at least in Balaenoptera), the an- 

 terior part of the bare bulla, without membranous covering, projects 

 into a fossa the size of one's two fists, and in freshly killed specimens 

 this is entirely filled with a coarse foam of albuminous, rather than 

 greasy, texture. Whether this is so in living specimens cannot be dem- 

 onstrated, but presumably it is, and the foam may have some function in 

 determining the quality of sound reception. There is free communica- 

 tion between this fossa and the choanae. In the odontocetes there is a 

 different but analogous system of air sinuses adjoining the inner ear and 

 connecting with an intricate labyrinth of ducts. Authors have been very 

 vague and cautious about describing these ducts, and with good reason, 

 for without the injection of a suitable colored mass into this part of a 

 freshly killed specimen their proper definition is uttterly impossible, as 

 their finer ramifications are otherwise not to be distinguished from ad- 

 joining blood vessels and oil ducts. It must therefore suffice to say that 

 this system of air sinuses communicate with the choanae and apparently 

 send trabeculated branches ramifying through the peculiar fatty tissue 

 that occurs in the odontocetes within the angle of the lower jaw. 



As already stated it is well known that cetaceans are sensitive to cer- 

 tain sorts of water borne vibrations. It has been reported that por- 

 poises are peculiarly sensitive to the waves that are transmitted by the 

 sonic depth finder and will disappear in great haste and apparent dis- 

 comfort form the vicinity of a vessel when one of these contrivances is 

 put in operation. This fact suggests that the Cetacea may be sensi- 

 tive to water-borne sound waves of a character and after a fashion that 

 we do not yet understand. The transmission of the sounds that reach 

 them and the ears themselves are so different from anything connected 

 with our own acoustic apparatus that my personal opinion is to the ef- 

 fect that we know nothing whatever about the matter. 



The function of a hydrostatic organ or depth gauge has been as- 

 signed to the air sinuses and passages about the cetacean ear, but it has 

 become the practice to assign this function to any part of cetacean an- 

 atomy which seems in any way unique or peculiar. I cannot see that 

 any sort of a hydrostatic organ would be necessary in this order, for they 

 can always tell when water pressure upon the body becomes too great 

 for comfort or safety. 



Numerous writers have concerned themselves with the question of 

 how the air within the inner ear is equalized to correspond with the 

 great external pressure experienced during deep diving. I cannot see 



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