ORGANS OF THE BODY. 655 



the membranous semicircular canals, which lie excentrically, that is, 

 attached to the convex aspect of the long passages (Riidinger), this elastic 

 lamina is maintained by the same observer to project in the form of 

 numerous tufts into the lumen. These, however, appear to be in man 

 pathological products (Lucae). Again, internally these present a thick 

 covering of epithelium (0'0068 mm. deep), made up of pavement cells, from 

 O'OOOO to 0'0180 mm. in diameter. From the usually numerous blood- 

 vessels of these walls a second watery 

 fluid is secreted, known as endolymph. 

 or aquula vitrea auditiva, which fills the 

 space contained within them. 



The otolithes (fig. 604), enclosed with- 

 in a special membrane, present them- 

 selves in the form of white specks at 

 those points where the terminal fila- 

 ments of the auditory nerves are spread 

 out in the sac of the vestibule. These 

 are probably small columnar crystals, 

 whose size varies to a remarkable extent, 

 their diameter ranging from O0090 to 

 0-0020 mm. and less. A few of them 

 re also contained within the membran- Fig. 604. otolithes, consisting of carbonate 

 ous semicircular canals. They consist 



principally of carbonate of calcium, but leave behind, according to the 

 observations of many investigators, an organic substratum, after having 

 been treated with acids. 



324. 



There now remains for our consideration the mode of distribution of the 

 acusticus to the two sacs of the vestibule and the membranous ampullae. 

 The nerve fibres for the sacculus hemiellipticus and ampullae are derived 

 from the n. vestibuli ; those for the sacculus rotundus from the so-called 

 n. saccularis minor, a branch of the cochlear division of the auditory. 

 They enter the duplicatures of the walls, which are especially distinct and 

 prominent in the ampullae, projecting into the cavity in the form of par- 

 titions. Here they divide into branches, and run towards the internal 

 free surface of the walls, still ramifying in their course. All the 

 nerve fibres are, however, confined to this projection, known as the 

 septum nerveum ; none of them extend into the adjacent parts of the 

 ampullae. 



It was formerly supposed, from the early investigations of Valentin and 

 Wagner, that the filaments of the auditory nerve were arranged in termi- 

 nal loops. The incorrectness of this view, however, is now generally 

 recognised ; and we know that the ends of the nerves undergo still farther 

 subdivision. It was Schultze, however, who first arrived at definite con- 

 clusions here in regard to the arrangement of parts, which latter is of the 

 highest interest, manifesting as it does such close relationship to the mode 

 of termination of the higher nerves of special sense (fig. 605). These 

 conclusions were not drawn from investigation of the structure of the 

 human ear, but from that of rays and sharks. 



If the septum nerveum be very minutely examined, its projecting 

 margin (crista acustica of Schultze) presents on either side a thick covering 

 of soft pultaceous matter, resembling, in transverse section, the cap of a 



