X44 PRACTICAL. CARP CULTURE. 



Next there is another chamber lying slightly above and in the i;ront 

 of the sac of the otoliths and consisting like it of an exceedingly delicate 

 transparent membrane. This is the central cavity or "vestibule," as it is 

 called in man. It usually contains a third otolith to which other branches 

 of the auditory nerve are attached and is filled, as is every part of the ear, 

 with the liquid already mentioned. It occupies most of the alcove orTe- 

 cess above spoken of except what is taken up by the sac of the otolith. 

 Connected with this vestibule are the three semicircular canals mentioned 

 in the description of the human ear. The foremost of these, the anterior, 

 rises from the front of the vestibule and in most fishes soon enters a tube 

 larger than itself in the parietal bone of the skull in which it loosely lies. 

 This tube curves backward and then downward and the canal within it of 

 course does the same until it at last emerges into the alcove of the ear and 

 reaches the membranous central cavity or vestibule at a point further 

 back than that from which it started. 



The second or posterior semicircular canal follows a similar course, 

 but its bony tube lies in the occipital or hindmost bone of the skull. This 

 is also vertical but in a "right-and-left," and not in a "fore-and-aft" 

 plane. One end of this canal enters the alcove of the ear by the same tube 

 which carries the bind end of the anterior canal. 



The third or exterior canal leaves the vestibule near the front and winds 

 horizontally backward in its bony tube to reenter it near its posterior end. 

 There are therefore five openings in the bone and five openings in the vest- 

 ibule for the passage of the six ends of the semicircular canals. Two of 

 them, as said above, unite before reaching the point of entrance. 



Each of these canals is expanded into a small bulb at one end. Two 

 of these bulbs are situated at the front and the third at the back of the 

 vestibule. All the above details can be seen represented in the figures ac- 

 companying this chapter. 



Thus then we see that the ear of the fish is in all essential points a true 

 ear, not a rudimentary ear, for the necessary portions might be still fur- 

 ther reduced, and yet leave the organ in a condition capable of translating 

 the vibrations of the outside medium into nerve vibrations. Any organ 

 capable of doing this is a true ear. Its most striking character is that it 

 is shut in and has no open channel of communication with the world out- 

 side. 



But the bones of the head form a medium by which vibrations or un- 

 dulations can be conducted inwards. It is, indeed, impossible to prevent 

 this inward conduction of all vibrations in the watery medium in which 

 the animal lives. Even some deaf men may be made to hear by putting 

 a tuning-fork to the teeth and so forming a solid line of connection be- 

 tween the fork and the inner ear. In the same manner a sound-vibration 

 in the water must be conducted through the skull-bones of a fish to its 

 inner ear deep sunk as it is at the base of the skull. 



Evidently the ear of a fish is not well adapted to receive the vibrations 

 of the air. These are very feeble in consequence of the lightness of that 

 medium. We ourselves do not hear sounds carried through the air when 



