522 STUDIES IN ADVANCED PHYSIOLOGY. 



4. Tectorium. From the lamina spiralis there extends 

 a membrane over the rods of Corti and reticular membrane 

 called the tectorium or tectorial membrane. It serves for 

 purposes of protection to these delicate structures under- 

 neath. The groove formed between the lower portions of 

 the lamina spiralis and the tectorial membrane is called the 

 sulcus spiralis. 



D 



Fig. 163. STRUCTURE OF A SINGLE ORGAN OF CORTI, AND TO THE RIGHT THEIR ARRANGE- 

 MENT INTO A SERIES, SUPPORTING THE FENESTRATED RETICULAR MEMBRANE. 



i, internal rod; e, external rod; t, articulation of the two rods; ft, beginning of reticu- 

 lar membrane; n, nerve; 6, basilar membrane. 



5. Auditory Hairs. This sulcus spiralis is lined with 

 cuboidal cells, which are continued over the margin of the 

 basilar membrane as columnar cells, some of which bear 

 on their upper end short, stiff hairs. These cells between 

 the rods of Corti and the sulcus spiralis are termed the 

 inner hair-cells. Similar cuboidal cells are found on the 

 basilar membrane beyond the rods of Corti, which cells end 

 in delicate stiff hairs that project through the openings in 

 the reticular membrane. These are called the outer hair- 

 cells. 



Where the basilar membrane joins the outer wall of the 

 cochlea these cells lose their cuboidal appearance and 

 gradually shade off into the ordinary epithelium which lines 

 the outer wall and the inner wall of the membrane of Reiss- 

 ner. These outer and inner hair-cells or auditory cells are 

 connected at their bases with nerve fibers from the auditory 

 nerve reaching them through the lamina spiralis. The 

 reader to orient himself properly must study the descrip- 

 tion just given in terms of the accompanying diagrams. 



