466 DISTRIBUTION OF THE AUDITORY NERVE. 



of four layers ; an external or serous layer, derived from the lining mem- 

 brane of the labyrinth ; a vascular layer, in which an abundance of minute 

 vessels are distributed ; a nervous layer, formed by the expansion of the 

 filaments of the vestibular nerve ; and an internal and serous membrane, 

 by which the limpid fluid which fills its interior is secreted. Some patches 

 of pigment have been observed by Mr. Wharton Jones in the tissue of the 

 membranous labyrinth of man. Among animals such spots are constant. 



The membranous labyrinth is filled w r ith a limpid fluid, first well de- 

 scribed by Scarpa, and thence named liquor Scarpse (endolymph,* vitreous 

 humour of the ear), and contains two small calcareous masses, called 

 otoconites. The otoconites (ou?, w<rog, x<ws, the ear-dust) consist of an 

 assemblage of minute, crystalline particles of carbonate and phosphate of 

 lime, held together by animal substance, and probably retained in form by 

 a reflection of the lining membrane of the membranous labyrinth. They 

 are found suspended in the liquor Scarpse ; one in the sacculus communis, 

 the other in the sacculus proprius, from that part of each sac with which 

 the nerves are connected. 



The AUDITORY NERVE divide's into two branches at the bottom of the 

 cul de sac of the meatus auditorius internus ; a vestibular nerve and a 

 cochlear nerve. The vestibular nerve, the most posterior of the two, divides 

 into three branches, superior, middle, and inferior. The superior vestibular 

 branch gives off a number of filaments which pass through the minute 

 openings of the eminentia pyramidalis and superior ventricle of the vesti- 

 bule, and are distributed to the sacculus communis and ampullae of the 

 perpendicular and horizontal semicircular canals. The middle vestibular 

 branch sends off numerous filaments, which pass through the openings of 

 the macula cribrosa in the anterior ventricle of the vestibule, and are dis- 

 tributed to the sacculus proprius. The inferior and smallest branch takes 

 its course backwards to the posterior wall of the vestibule, and gives off 

 filaments which pierce the wall of the ampullary dilatation of the oblique 

 canal to be distributed upon its ampulla. According to Stiefensand there 

 is in the situation of the point of entrance of the nervous filaments into the 

 ampulla a deep depression upon the exterior of the membrane, and upon 

 the interior a corresponding projection, which forms a kind of transverse 

 septum, partially dividing the cavity of the ampulla into two chambers. 

 In the substance of the sacculi and ampullae, the nervous filaments radiate 

 in all directions, anastomosing with each other and forming interlacements 

 and loops, and they terminate upon the inner surface of the membrane in 

 minute papillae, resembling those of the retina. 



The Cochlear nerve divides into numerous filaments which enter the 

 ^foramina of the tractus spiralis foraminulentus in the base of the cochlea, 

 and passing upwards in the canals of the modiolus, bend outwards at right 

 angles, to be distributed in the tissue of the lamina spiralis. The central 

 portion of the nerve passes through the tubulus centralis of the modiolus, 

 and supplies the apicial portion of the lamina spiralis. In the lamina 

 spiralis the nervous filaments lying side by side on an even plane form 

 numerous anastomosing loops, and spread out into a nervous membrane. 



* Antonio Scarpa is celebrated for several beautiful surgical and anatomical mono- 

 giaphs; as, for example, bis work on "Aneurism," " De Auditu et Olfactu," &c. An 

 eccoiint of the aqua labyririthi will be found in his anatomical observations " De Struc- 

 :rta Fenestra3 JRotundte, et de Tympano Secvmdaria." 



