326 ELEMENTS OF HISTOLOGY. [Chap. XLI. 



space by an osseous projection the lamina spiralis 

 ossea and by the scala media into two scalse, viz., the 

 (upper) scala vestibuli, and the (lower) scala lympani. 



467. In the osseous modiolus are numerous paral- 

 lel canals for bundles or groups of the fibres of the 

 cochlear branch of the auditory nerve ; these canals 

 open into the porus internus, in which lies a large 

 ganglion connected with the nerve. 



The nerve bundles situated in the canals of the 

 modiolus, corresponding to the lamina spiralis ossea, 

 are connected with ganglionic masses composed of 

 bipolar ganglion cells called the ganglion spirale of 

 Corti. From this ganglionic mass the nerve-fibres (all 

 medullated) can be traced into the lamina spiralis 

 ossea, in which they form rich plexuses extending to 

 the margin of this lamina i.e., to the membrana 

 basilaris of the scala media (see below). 



468. From the margin of the lamina spiralis ossea 

 to the external bony shell extends the membrana basi- 

 laris (Fig. 163), forming the lower and chief wall of 

 the scala media, while the upper wall of the canal is 

 formed by the membrane of Reissner, extending 

 under an acute angle from near the margin of the 

 lamina spiralis ossea to the outer bony shell. 



On a transverse section through the scala media 

 we see the following structures : 



469. (1) Its outer wall is placed close against 

 the periosteum lining the internal surface of the bony 

 shell ; it consists of lamellar fibrous tissue, with 

 numerous stiff elastic bands, and is the vestibular 

 part of a peculiar ligament the ligamentum spirale 

 (Kolliker) semi-lunar in cross section, and with its 

 middle angular projection fixed to the outer end of 

 the membrana basilaris. 



470. (2) Its inner wall is represented by an 

 exceedingly delicate membrane the membrane of 

 Reissner ; this is also its upper wall, extending under 



