COCHLEA. 



471 



extended over the whole of the lamina spiralis. Thus is the 

 auditory nerve distributed. 



The central portion of the modiolus, which contains a 

 great number of minute canals, was called by Scarpa the trhctus 

 spiralis for aminulosus. The nerves of the cochlea enter these 

 canals and pass out successively at right angles between the 

 two bony plates forming the zona ossea of the lamina spiralis, 

 to be expanded on the membranous portion of the lamina. 

 The nervous pulp is expanded in a naked state, and the neurile- 

 ma which it throws off, forms, according to Breschet, the basis 

 of the membranous structure of the lamina spiralis. 



Fig. 203 * 



To complete the account of the labyrinth, it is to be observed 

 that a pellucid fluid certainly exists in it, exterior to the sacs 



* Fig. 203, is a vertical section of the cochlea made through its axis in 

 order to exhibit its internal structure, much magnified, a a a. Branch of the 

 auditory nerve to the cochlea (nervus cochkaris), over which the veins are seen 

 running and penetrating in small branches through the lamina spiralis. The 

 arteries are not shown here, but they have the same course as the veins, b, 

 Filaments of the nerve, lodged in the zona ossea of the cochlea, c c, Anasto- 

 moses of the filaments of the nerve with one another in the form of loops, in 

 the zona media, d, The neurilema abandoning the nervous loops, in order to 

 form, according to Breschet, the zona membranosa. The blood-vessels are 



