262 



ANIMAL PHYSIOLOGY. 



in the osseous canals of the same name, and likewise exhibit 

 each an ampulla. The fluid in which all these membranous 

 structures float is called the peri- 

 lymph, and that which they contain 

 is called the endolympli. The nerves 

 are supplied only to limited portions 

 of the membranous vestibule, one 

 branch passing to the saccule, an- 

 other to the utricle, and one to a 

 little crescentic elevation projecting 

 into the interior of each ampulla. 

 The interior of the membranous 

 vestibule is lined with epithelium; 

 and exceedingly slender straight 

 hairs project through the epithelium 

 at the parts supplied with nerves, 

 and are probably in continuity with 

 the nerve fibres. These hairs may 

 be supposed to vibrate with sono- 

 rous vibrations; and to make such 

 " vibrations stronger, there is a collec- 

 tion of minute crystals of carbonate 

 of lime, the otoliths or otoconia, in 

 the neighbourhood of the termina- 

 tion of each branch of nerve. 

 Fig. 130. NERVE-TERMI- 194. The cochlea is, in its early 

 NATIONS IN AN AMPULLA, development, an outgrowth from the 

 ^MTullir'ner"; -stibule, and as it elongates it 

 fibres; &,&,fusiform cells; becomes spirally coiled, taking two 

 c, c, auditory hairs, complete turns and a half, tapering 

 Rildinger, ^ ^ extremity, and acquiring, as 



has already been remarked, the appearance of a snail's 

 shell. The base of the shell is at the perforated plate of 

 the inner auditory meatus, the apex abuts' against the 

 tympanic end of the Eustachian tube,, the mouth is in 

 connection with the vestibule, and in the centre of the 

 coils of the tube is a pillar of bone, the modiolus, pierced 

 with canals containing the cochlear branches of nerve. Around 

 the modiolus is a spiral ledge of bone, the lamina spiralis, pro 

 jecting into the interior of the tube; and continued directly 



