376 ELEMENTARY PHYSIOLOGY less. 



the summit the scala tympani, along which they descend, 

 and are eventually lost at the fenestra rotunda in which 

 that scala ends. 



(vii) The Organ of Corti. — But besides this peculiar 

 arrangement of the perilymph chamber, there are other 

 and still more important differences between the cochlea 

 and the labyrinth. 



The auditory nerve is, as we have seen, distributed to 

 certain parts only of the membranous labyrinth, namely, 

 to the crests of the ampulliB and to the patches on the 

 utricle and the saccule ; but, in the case of the cochlea, 

 fibres, running in canals excavated in the bony core of the 

 spiral, and in the lamina spiralis (Fig. 121, A.N) run 

 to and end in the canalis cochlearis along its whole length, 

 from the bottom to the top of the spiral, Fig. 124, Coch. 

 And the mode of ending of these nerves is very peculiar. 



If we examine a section of one of the spirals of the 

 cochlea (Fig. 121), we see that the upper side of the 

 cochlear tube (that which separates it from the scala vesti- 

 buli) i.s formed by a thin membrane (called the membrane 

 of Reissner, Fig. 121, m.R) lined internally by simple 

 epithelium. The outer convex side of the! cochlear tube, 

 that side by which it is firmly attached to the bony wall, 

 is also lined internally by simple epithelium. Neither 

 here nor in the membrane of Reissner do any fibres of the 

 auditory nerve end. But the remaining side of the 

 tube, that which looks towards the scala tympani, 

 possesses on its inner face, along the whole length 

 of the tube, from the bottom to the top of the spiral, 

 a very remarkable and strangely modified epithelium ; 

 and, along the whole length of the tube, fibres of 

 the auditory nerve pass into and end among the cells 

 of this epithelium, which is spoken of as the organ of 

 Corti. (Fig. 121, 0.0.) 



The membrane which separates the cavity of the 

 cochlear tube from the scala tympani, and on which the 

 organ of Corti is placed, is of a peculiar character, speci- 



