392 



NORMAL HISTOLOGY. 



The basilar membrane includes three distinct layers, the epithe- 

 lium, the substantia propria, and the tympanic lamella. The 

 substantia or membrana propria consists of almost homoge- 

 neous connective tissue, and represents an enormously-developed 

 basement-membrane beneath the highly-specialized epithelium of the 

 tympanic wall. This stratum is covered by a layer of peculiar con- 

 nective tissue, the tympanic lamella, directly continuous with the 

 tympanic periosteum. 



The lamella contains numbers of fusiform cells of immature 

 character interspersed with fibres ; in this position the differentiation 



of the mesodermic cells 

 lining the tympanic 

 canal has never ad- 

 vanced to the produc- 

 tion of typical endo- 

 thelial plates, the free 

 surface of the lamella 

 being invested by the 



short fusiform cells 

 alone. 



The epithelium 

 covering the basilar 

 membrane within the 

 inner zone forms the 

 remarkable organ of 

 Corti, the highest ex- 

 ample of specialization 

 of neuro - epithelium 



Section of Corti's organ from guinea-pig's cochlea : ST, scala 

 tympani ; TC, tunnel of Corti ; a, bony tis-.uo of spiral lamina ; 

 b, fibrous tissue covering same continued as substantia propria 

 of basilar membrane ; c, c 1 ', protoplasmic envelope of Corti's 

 pillars (e, e') d, endothelial plates ; /, heads of pillars contain- 

 ing oval areas ; g, head-plates of pillars ; h, K , inner and outer 

 hair-cells; in, membrana reticularis; k, I, cells of Hensen and 

 of Claudius ; n, nerve-fibres ; i, cells of Deiters. 



anywhere encountered. 



The organ of Corti extends the entire length of the cochlear duct, 

 v \vith the exception of a short distance within the blind terminal sacs 

 at the two ends of the canal, where the neuro-epithelium is wanting. 

 In general it consists of a series of epithelial arches formed by 

 the interlocking of the ends of two converging greatly modified 

 epithelial cells, the pillars or rods of Corti, upon the inner and 

 outer sides of which rest groups of neuro-epithelium ; the tri- 

 angular space included between the converging pillars of Corti above 

 and the basilar membrane below constitutes the tunnel of Corti, 

 which is, therefore, only an intercellular space of unusual size, 

 containing probably a soft semi-fluid intercellular substance serving 

 to support the nerve-fibrils traversing the space. 



Examined in detail, the pillars or rods of Corti prove to be com- 

 posed of two parts, the denser substance of the pillar proper 

 and a thin imperfect protoplasmic envelope, which presents a 



