XXXIII.] 



THE COCHLEA. 



373 



an upper scala vestibuli and a lower compartment scala tym- 

 pani ; the central column or modiolus ; the last is osseous and 

 contains channels for nerves and vessels. The lamina spiralis is 

 partly osseous, viz., that part next the modiolus, and partly mem- 

 branous, viz., that part next the wall of the cochlea; the latter 

 part is the membrana basilaris. The osseous portion terminates 

 in a crest the crista spiralis and its free end is scooped out into 

 a groove sulcus spiralis. 



(!>.) From the upper surface of the lamina spiralis ossea there 

 runs to the wall of the cochlea a thin membrane membrane oi 



FIG. 343. Scheme of the Canalis Cochlearis and the Organ of Corti. N. Cochlear nerve ; 

 t. Inner row, and p. Outer rows of hair-cells; n. Nerve-fibrils terminating in p\ 

 a. Supporting cells for p\ d Cells in the sulcus spiralis ; G aud //. Epithelial cells ; 

 o. Membrana reticularis ; z. Inner, and y. Outer Rod of Corti. 



Reissner which completely shuts off a small three-sided cavity 

 from the scala vestibuli. This is the ductus cochlearis, canalis 

 cochlearis, or scala media. It is bounded by the wall of the cochlea, 

 the membrane of Reissner and its base is formed by the outer 

 part of the osseous and the whole of the membranous spiral lamina. 

 The latter is called the basilar membrane. This cavity contains 

 a fluid, the endolymph, and into it pass the cochlear branches of the 

 auditory nerve to end in a complex structure organ of Corti 

 which rests on the basilar membrane. 



(c.) Note in the scala media a membrane membrana tectoria 



