662 PISCES. 



(1829.) The ears of fishes, therefore, are much less perfect than those 

 of other Vertebrata* : deprived of tympanum, of ossicles, and of Eusta- 

 chian 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 moreover, the membranous 

 labyrinth not being enclosed in bone, the skull can only transmit these 

 movements in a very feeble and imperfect 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 mem- 

 branous apparatus endowed with great sensibility, in which the nervous 

 filaments distributed 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 

 otoliths contained in its cavities. 



(1830.) It is probable, therefore, that fishes hear, that noise pro- 

 duces in them a powerful sensation, but that they cannot distinguish 

 or appreciate differences of tone, as the higher animals are enabled to do. 



(1831.) The nerves composing the eighth pair preside over the same 

 functions in all the Vertebrata. The glosso-pharyngedl sends twigs to 

 the first branchial arch, the fauces, and the tongue. The nervus vagus 

 (fig. 319, 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, how- 

 ever, it likewise furnishes nerves to other parts of the body, especially 

 a long branch, which generally runs in the substance of the lateral 

 muscles of the trunk, communicating with the spinal nerves and giving 

 off filaments to the skin an arrangement the physiology of which is not 

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

 under consideration would seem to represent the spinal recurrent of the 

 human subject ; it supplies the swimming-bladder and the muscles of 

 the shoulder. 



(1832.) All the above nerves posterior to the optic arise from a chain 

 of ganglia constituting the medulla oblongata but above these are 

 situated other important masses entering into the composition of the 

 encephalon, from which no nerves take their origin, viz. the cerebral 

 hemispheres and the cerebellum. 



(1833.) The cerebral hemispheres in all the Vertebrata are undoubt- 

 edly the seat of the mental powers ; and as this portion of the brain 

 becomes developed and perfected, brutality and stupidity give place to 

 sagacity and intelligence. 



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



