238 THE NERVOUS SYSTEM. 



The outer wall of the scala media is lined with a single 

 layer of epithelium-cells, varying from squamous to columnar, 

 which rest on the ligamentum spirale, a fibrous cushion lying 

 against the bony walls on the outer side of the cochlea; a 

 portion of this outer wall (" stria vascularis ") is very 

 vascular. 



The floor or lower wall of the scala media is formed by the 

 margin or limbus of the lamina spiralis, the basilar membrane, 

 and columnar and neuro-epithelium (the organ of Corti) rest- 

 ing on the latter. The margin of the bony spiral lamina is 

 thickened by the development on its upper surface of a mass 

 of fibrous tissue, the whole forming the limbus. 



The outer projecting aspect of the limbus is hollowed 

 into a groove, the sulcus spiralis, the upper lip of which 

 is called the labium vestibulare, the lower lip the labium tym- 

 panicum. 



The labium vestibulare is divided by clefts into fine proc- 

 esses called the " auditory teeth." 



The membrana basilaris is a connective-tissue lamina ex- 

 tending from the labium tympanicum of the limbus across to 

 the ligamentum spirale on the outer wall, shutting off' the 

 scala media from the scala tympani ; it is lined underneath 

 (within the scala tympani) with endothelium, while its upper 

 surface is covered with columnar epithelium and the neuro- 

 epithelium constituting the organ of Corti. 



The upper surface of the limbus is lined with simple squam- 

 ous epithelium continuous with that lining the membrane of 

 Reissner. 



The sulcus spiralis is lined with a layer of columnar epithe- 

 lium-cells, which extend to the inner hair-cells or inner margin 

 of the organ of Corti. 



The organ of Corti (Fig. 94) : These inner hair-cells 

 comprise a single row of columnar epithelium-cells, with a 

 number of filaments or hairs projecting from their free ends ; 

 they are adjacent to and on the inner side of the pillars of 

 Corti, their attached ends not extending to the basilar mem- 

 brane. 



The pillars or rods of Corti are two rows of elongated 

 epithelial elements, the lower ends of which rest on the basilar 

 membrane some distance apart, and whose upper ends are 



