264 



ANIMAL PHYSIOLOGY. 



canalis membranacea. It will be understood from tins that 

 tlie two scalse are filled with perilymph, while the canalis 

 membranacea is lined with epithelium, and contains endo- 

 lymph. 



Fig. 132. ORGAN OF CORTI, diagrammatic view, a, Basilar mem- 

 brane; b, tough structure attached to the edge of the osseous 

 lamina spiralis, termed its limbus, and presenting a toothed 

 appearance; c, membrane of Keissner; d, d, membrana tectoria; 

 e, nerve perforating the basilar membrane ; /, /, epithelial cells ; 

 g, h, inner and outer groups of ciliated or hair-bearing cells; i, k t 

 inner and outer rods of Corti ; I, membrana velamentosa. 



In the interior of the canalis membranacea, situated on 

 the basilar membrane, is the sensitive part of the cochlea, an 

 exceedingly complicated structure called the organ of Corti. 

 This organ contains numerous sets of nucleated cells, some of 

 them furnished with stiff cilia or hairs, and it is permeated 

 with very fine ramifications of the cochlear nerve; and it also 

 contains an outer and inner range of very remarkable strap- 

 shaped structures of comparatively tough consistence, one 

 range leaning against the other, like the rafters of a house. 

 These strap-shaped structures are called the rods of Corti. It 

 is curious to note that, while the osseous cochlea diminishes 

 from base to apex, these rods increase in length (Urban 

 Pritchard), and the basilar membrane on which they lie 

 increases in breadth as the apex is approached (Henle). 



195. It is difficult to understand the exact mode of action 

 of the different parts of the internal ear. It has been long 

 generally assumed that the semicircular canals are useful 

 in determining the directions whence sounds proceed, and 



