NERVE 



171 



at the round window. They communicate with one another 

 through a small opening at the apex, the helicotrema. 



The semicircular canals (iig. 54) also open from the 

 vestibule. Their functions have been discussed (p. 121). 



A complex membranous bag, the membranous labyrinth, lies 

 in the perilymph of the bony labyrinth. This has an outer 

 fibrous coat, and inside this a homogeneous laver. 



In the vestibule the membranous labyrinth consists of the 

 utricle and saccule, the functions of which are related to 



/ B.M. 



Fig. 85. — Transverse Section through one turn of the Cochlea to show the 

 Organ of Corti on the Basilar Membrane. S.M., scala media; S.V., 

 scala vestibuli ; S.T., scala tympani. The tectorial membrane 

 normally lies upon the hair cells of Cortis organ. 



those of the canals. From the saccule a narrow canalis 

 reuniens runs to the membranous cochlea, which lies upon 

 the basilar membrane, as the scala media, between the scala 

 vestibuli and scala tympani and ends blindly at the apex of 

 the cochlea (fig. 85, S.M.). 



In the membranous cochlea, the organ of Corti (fig. 85) is 

 formed by a special development of the epithelium lining the 

 tube. It is set upon the inner more elastic part of the 

 basilar membrane, and consists from within, outwards, of — 

 1st. A set of elongated supporting cells; 2nd. A row of 

 columnar cells, with short, stiff, hair-like processes projecting 



