HEARING. o9.3 



appendage (c) termed the Cyslicule. The hard 

 calcareous bodies (o, o, o) are three in number;* 

 and the branches of nerves (i, i, i), by which they 

 are suspended in the fluid contained in the mem- 

 branes, are seen passing into them ; while the 

 ampullae are supplied by other branches (n, n, n). 

 In all the osseous fishes the labyrinth is not en- 

 closed in the bones of the cranium, but projects into 

 its cavity; but in the larger cartilaginous fishes, as 

 the Ray and Shark tribes, it is surrounded by solid 

 bone, and is not visible within the cranium. In 

 these latter fishes, we first meet with a rudiment of 

 the meatus, in a long passage extending from the 

 inner side of the vestibule to the upper and back 

 part of the skull ; where it is closed by a mem- 

 brane, which is covered by the skin.^ 



Aquatic reptiles have ears constructed nearly on 

 the same plan as those of fishes ; thus the Triton 

 or Newt, has a vestibule containing only one cre- 

 taceous body, and three semicircular canals, un- 

 protected by any surrounding bone. In the Frog, 

 however, we first perceive the addition of a distinct 

 cavity, closed by a membrane, which is on a level 

 with the integuments, on each side of the head. 

 From this cavity, which corresponds to that of the 

 tympanum, there proceeds an Eustachian tube, 

 and within it, extending from the external mem- 



* The shape of these otoHthes is so definite in osseous fishes, as to 

 be capable of furnishing, according to Cuvier, characters available 

 for the determination of species. They are considered by Weber as 

 supplying the place of the cochlea in this class of animals, and of 

 making direct impressions on the auditory nerves. See Todd's 

 Cycl. ii, 567. 



t Scarpa and others do not consider these passages as performing 

 the office of auditory canals. 



