SENSE ORGANS. 



177 



branous labyrinth is a membranous apparatus lodged in 

 these cavities. Each of these two parts consists of 

 three parts, viz., the vestibule, the semicircular canals, and 

 the cochlea. There is therefore a bony vestibule, semi- 

 circular canals, and cochlea, and a membranous vesti- 

 bule (vestibular sac), semicircular canals, and cochlea. 

 All these parts in the membranous apparatus have forms 

 similar to the bony cavity in which they are lodged, but 

 are much smaller, so that there is considerable space be- 

 tween the true receptive membranous part and the cav- 



t.tm. 



Fig. in. — Outer and middle ear seen in section, and the inner as a cast of 

 the bony labyrinth : ma, meatus auditorius ; mc, mastoid cells ; t, tym- 

 panic membrane ; m, malleus ; i, the incus ; v, vestibule ; c, cochlea ; 

 sc, semicircular canals ; aun, auditory nerve. (After Cleland.) 



ity in which it is lodged. This space is filled with a 

 watery liquid called perilymph. The membranous ap- 

 paratus is also filled with a liquid called endolymph. In 

 the diagram (Fig. 109) the dotted parts represent the 

 membranous labyrinth. 



