THE MEMBEAXOUS COCHLEA. 655 



When the limbns is visTved fi'om aboYc, the edge is seen to present, not a 

 continuous line, but a succession of tooth-like projections (fig. 470, Cr), 

 which give it a jagged aspect. These projections are continued as 

 flattened eminences a short distance on the upper surface of the limbus, 

 which is, therefore, not smooth, but, at least near the edge, marked 

 in this way with eminences and intervening furrows. Nearer the 

 line of origin of the membrane of Reissner, however, it becomes 

 more uniform, and here, too, its epithelial covering, which is directly 

 continuous with that of the under surface of Eeissner's membrane, is 

 evenly distributed ; whereas at the crest itself the epithelial cells are, 

 in the adult, only found in the furrows : so that the tooth-like promi- 

 nences project between the rows of epithelium into the cochlear canal. 

 Immediately below the overhanging projections, the epithelium again 

 runs together into a uniform single layer which lines the spiral groove, 

 and is continuous externally with the more specialized cells, presently 

 to be described as forming the organ of Corti. 



The basilar membrane stretches, as before-mentioned, straight 

 between the osseous lamina and the spiral ligament on the outer wall, 

 and separates the canal of the cochlea from the scala tympani. It 

 increases in breadth from the base to the apex of the cochlea, while the 

 breadth of the osseous spiral lamina diminishes. Thus in the first turn 

 of the cochlea, this membrane fonns about half of the breadth of the 

 septum made by it and the osseous lamina ; but towards the apex of 

 the cochlea the proportion between the two parts is gradually changed, 

 until, near the helioctrema, the membranous part is left almost unsup- 



Fig. 470. 



Fig. 470. — Semi-diagrammatic View of part of the Basilar IMembrane axd Tuxxel 



OF COKTI OF THE KabBIT, FROM ABO.VE AND THE SIDE. Much magnified. 



I, limbus ; Cr, extremity or crest of limbus with tooth-like projections ; h b, basilar 

 membrane ; p, perforations for transmission of nerve fibres N, which are represented at 

 the lower part of the figure, but omitted for the sake of clearness in the ujjper ; i.r, fif- 

 teen of the inner rods of Corti ; h.i, their flattened heads seen from above ; c.r, nine 

 outer rods of Corti ; h.e, their heads, with the phalangeal processes extending outward 

 from them and forming, with the two rows of phalanges, the lamina reticularis, I. r. The 

 fibres of the outer rods are seen to be continued into the striation of the basilar mem- 

 brane, through which the connective tissue fibres and nuclei of the undermost layer are 

 seen. Portions of a few of the basilar processes of the outer hair-cells remain att?.ched 

 to the membrane. 



