466 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



by the Cetacea, which, at most, have nothing more 

 than an exceedingly rudimentary external ear (pinna), 

 and this, when found in these mammals, is proportion- 

 ately longer in the fretus than in the adult (Howse). 



Fig. 197. Representation of the Human Ear. 



e, External ear; me, auditory passage (meatus auditorius externus); I, bony 

 labyrinth; ym, auditory nerve ; o, ossicles of the ear:/o, fenestra ovalis; 

 eu, Eustachiafl tube, which opens into the pharynx ; t, tympanum ; c, bony 

 cochlea ; tin, tympauic membrane. 



Fishes are without any external ear or tympanic 

 membrane, and, as has already been said, the Elasmo- 

 branchs have a canal which reaches to, and may open 

 on, the outer surface of the skull j in many Teleostei, 

 where there is no such external opening, there are 

 spaces in the skull which are only covered by skin or 

 very thin bone in the neighbourhood of the ear ; 

 in some of the bony fishes there is an exceedingly 



