444 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



sists of a spirally arranged tube which forms from 

 two and one-half to two and three-quarter coils 

 around a central pillar termed the modiolus. The 

 length of this tube is about 30 mm. and its diameter, 

 near the base of the cochlea, about 2 mm. The 



Scala 



vestibuli. ^sari:M : .i x i^f&oiranKmvimmi .'JtwtssKf ir.M^sw ^. i 



ganglion. 



Cochlea 

 duct. 



Scala 

 tympani 



Osseous cochlear wall. Nervus cochlearis. 



Fig. 306. Longitudinal section of the cochlea of a cat. This figure 

 gives a general view of the cochlea. The cochlear duct is met with six 

 times in the section (Sobotta). 



modiolus is about 3 mm. in height and transmits the 

 nerve. A flat shelf of bone, the lamina spiralis, 

 winds around the modiolus like the thread of a screw, 

 and projects about half-way into the cochlear tube 

 and thus incompletely divides this tube into two 

 passages, of which the upper is named the scala vesti- 



