TERMINATION OF NERVES IN VESTIBULE. 399 



The area of distribution of the acoustic nerve in the 

 vestibule and semicircular canals is limited to five spots, — 

 one situated respectively in each division of this part of the 

 membranous labyrinth ; namely, the Saccule, Utricle, and 

 three ampullse. In the latter the area of distribution is 

 raised into a kind of ridge or crest, and for this reason was 

 named by Max Schultze the Crista Acustica; whereas in 

 the Saccule and Utricle it is merely an oval spot, and has 

 received the name of the Macula Acustica from the same 

 author. 



In the region of these acoustic ridges and spots the mem- 

 branous labyrinth is firmly adherent, by means of a layer 

 of dense connective tissue, to the bony wall, not being 

 separated by the epilymph as in other parts of the labyrinth, 

 and the membrane itself is specially modified in structure. 



Speaking generally this membrane consists of three 

 parts ; externally an irregular layer of loose connective 

 tissue ; next a dense layer of the same tissue, frequently 

 called the Tunica Propria ^ and lastly a single layer of 

 tesselated epithelial cells. At the acoustic spots the outer 

 layer is lost, becoming blended with the periosteum, which 

 in many animals (sheep, guinea pigs, &c.), here presents a 

 layer of branched pigment cells, such as are found in the 

 choroid coat of the eyeball. The tunica propria remains 

 almost unchanged, but in the epithelial layer are to be 

 found some very remarkable modifications. 



The tesselated cells as they approach the acoustic spot 

 gradually increase in thickness, and become first cuboid 

 and then columnar, in which form they are found on the 

 margin of the acoustic spot, where they are changed into 

 nerve-epithelium. But before proceeding to the detailed 

 account of this structure, I must mention that scattered 

 somewhat irregularly amongst the columnar epithelium are 

 found (according to Hasse, Odenius, and Meyer), peculiar 

 pigmented fibro-granular cells with small summits and ex- 

 tending bases, which frequently meet, giving the appear- 

 ance of a pigmented network when looking at the membrane 

 from above ; these cells appear to be similar to those found 

 so abundantly in the tegumentum of the bird's cochlea. 



ITie Nerve-Epithelium. 



Max Schultze in 1858 described this strncture in the 

 fishes as consisting of three epithelial forms. A deep layer 

 of nuclei which comes next to the tunica propria, these he 

 called the Basalzellen ; a superficial layer of cylindrical cells, 

 Cylinderzellen ; and numerous nuclei between them, sur- 



