DISTRIBUTION OF THE AUDITORY NERVE. 461 



means of the numerous nervous filaments which are distributed to it 

 from the openings in the inner wall of the vestibule, and is separated 

 from the lining membrane of the labyrinth by the aqua labyrinthi. 



The structure of the membranous labyrinth is composed 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 ex- 

 pansion of the filaments of the vestibular nerve and of an internal 

 and serous membrane, by which the limpid fluid which fills the 

 membranous labyrinth is secreted. Some small patches of pigment 

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

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



The membranous labyrinth is filled in the interior with a limpid 

 fluid, first well described by Scarpa, and thence named liquor 

 Scarpce* (endolymph, vitreous humour of the ear,) and contains two 

 small calcareous masses called otoconites. The otoconites (ouV, urog 

 xo'vis, 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, and the other 

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

 nerves are connected. 



The AUDITORY NERVE divides 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 of the superior ventricle of the vestibule, and are distributed to 

 the sacculus communis, and to the 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 

 distributed to the sacculus proprius. The inferior and smallest 

 branch takes its course backwards to the posterior wall of the vesti- 

 bule, 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 ampullae a deep depression 

 upon the exterior of the membrane, and upon the interior a corre- 

 sponding projection, which forms a kind of transverse septum, par- 

 tially dividing the cavity of the ampulla into two chambers. 



Upon entering the structure of the sacculi and ampullae, the ner- 

 vous filaments radiate in all directions, anastomosing with each 



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

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

 account of the aqua labyrinthi will be found in his anatomical observations "De Struc- 

 tura Fenestraa Rotunda, ct de Tympano Sccundario." 



