THE KAK. 



(1) The walls of the membranous labyrinth have the same 

 general structure throughout : the walls are usually thicker at 

 the nerve terminations, in the ampullae, semicircular canals, pars 

 neglecta, and especially the pars basilaris ; the wall of the tegn>t>ttinit 

 lympani are the thinnest. The walls are transparent, homogeneous, 

 refractive, and, at places, show a faint striation, which is, as a rule, 

 mt due to the presence of fibres; in parts of the recessu* utricitfi, 

 and in the outer wall of the saccate, especially near the 1 eg at en f inn 

 rasciifowm, more or less distinct fibres can be made out. Sections 

 of the wall show spindle-shaped cells, with the processes usually 

 arranged parallel to the surfaces; seen from the surface, the cells 

 are seen to branch in all directions (Fig. 251 I, II). In the 

 thinner parts of the walls the cells are few or altogether absent. 

 The outer surface of the membranous labyrinth is uneven, in conse- 

 quence of the attachment of the perilymphatic network. Blood- 

 vessels are also attached to the outer surface, and pierce the wall, 

 especially near the nerve-terminations. 



The whole of the inner surface is lined with a layer of polygonal, 

 tesselated epithelium-cells. The size and height of the epithelium 

 varies in different parts. On the outer wall of the saccule the cells 

 are large, but on the inner wall small ; they are also large in the 

 semicircular canals, except on a small raphe on the inner and outer 

 side, where they are smaller but higher (Fig. 251 re}; in the am- 

 pullae the cells are large, except on the roof. In the utricle and 

 xlnu* superior they are also moderately large. In addition to the places 

 mentioned, a smaller epithelium is found on the floors of the am- 

 pullae, in the recessns iitriculi, and near all the nerve-terminations 

 and on the sides of the ampullar septa. Surrounding the nerve- 

 terminations of the macula rec. utriculi, macula sacculi, and jMpllla 

 lagenae are found narrow, branched, yellowish cells (Fig. 251 pe) 

 with spindle-shaped nuclei. Cells of a third kind, first described 

 by Deiters, Hasse, and Kulin, in the tegi/ientinn raxciilo*tnii, and in 

 the ampullae by Hasse and Kuhn, are also found in the utricle. 

 They contain a yellowish pigment, and are collected into two 

 sharply differentiated groups in each ampulla (Hasse has one placed 

 before and one behind the septum on the floor). The cells are 

 cylindrical; the upper parts striated, the lower narrower, and the 

 bases again widened to a polygonal, more homogeneous plate, 

 which is fixed to the wall. On the tegmentiim i-ascif?o*um the corre- 

 sponding cells are not so high. 



(2) The nerve-terminations. The larger branches of the auditory 



D d 2 



