528 PISCES FISHES. 



iS distributed over the vestibular sacculus, where it forms a beauti- 

 ful net-work. 



There is.no Cochlea, although some writers imagine that they 

 can distinguish a rudiment of this part of the ear in a slight pro- 

 jection from the walls of the vestibule. 



(569.) The ears of fishes are, therefore, much less perfect than 

 those of other Vertebrata : * deprived of tympanum, of ossicles, 

 and of Eustachian tube, they can scarcely receive the impressions 

 produced by the vibrations of the ambient element, except by those 

 vibrations being communicated through the cranium ; and, more- 

 over, the membranous labyrinth not being enclosed in bone, the 

 skull can only transmit these movements in a very feeble and im- 

 perfect manner. The absence of a cochlea would go far to prove 

 that the ear of fishes cannot appreciate the differences of tones. All 

 that it offers to the physiologist is a membranous apparatus en- 

 dowed with great sensibility, in which the nervous filaments distri- 

 buted in the ampullae of the semicircular canals must necessarily 

 partake of all the movements of the fluid in which they are 

 plunged, and where those appropriated to the vestibule must be 

 still more strongly agitated by the shocks that these movements 

 give to the otolithes contained in its cavities. 



It is probable, therefore, that fishes hear ; that noise produces in 

 them a powerful sensation ; but that they cannot distinguish or 

 appreciate differences of tone, as the higher animals are enabled 

 to do. 



(570.) The nerves composing the eighth pair, preside over the 

 same functions in all the Vertebrata. The glosso-pharyngeal sends 

 twigs to the first branchial arch, the fauces, and the tongue. The 

 nervus vagus (Jig. 222, t) supplies the three posterior branchiae, 

 and the lower part of the pharynx; it is then continued along the 

 (oesophagus to the stomach, where it terminates : it thus presides 

 over the same functions in all the Vertebrate classes ; and it is not 

 a little interesting to see it even in fishes distributed to the organs 

 of respiration, notwithstanding the peculiarity of their structure 

 and position. In these creatures, however, it likewise furnishes 

 nerves to other parts of the body, and sends a long branch, 

 which generally runs in the substance of the lateral muscles of the 

 trunk, communicating with the spinal nerves, and giving off fila- 

 ments to the skin ; an arrangement the physiology of which is not 

 as yet understood. The next pair of cerebral nerves in the ani- 



* Cuv. et Val. op. cit. p. 347. 



