758 THE EAE. 



in the lower and fore part of the cavity of the osseous vestibule, close to 

 the opening from the scala vestibuli of the cochlea, and is received into the 

 hollow of the fovea hemispherica, from the bottom of which many branches 

 of nerve enter. The sacculus appears to have a cavity distinct from that 

 of the utricle, but is filled with the like thin and clear fluid, endolymph, and 

 contains similar otoconia in its wall. It is prolonged below into a short 

 narrow duct, canalis reuniens, which opens abruptly into the membranous 

 canal of the cochlea. 



Fig. 513. 

 A. B. 



Fig. 513. VIEWS OF THE INTERIOR OF THE RIGHT LABYRINTH WITH ITS MEMBRANOUS 

 PARTS AND NERVES (from Breschet). f 



A, the outer wall of the osseous labyrinth in part removed so as to display the mem- 

 branous parts within. 1, commencement of the spiral tube of the cochlea ; 2, posterior 

 semicircular canal partially opened, showing its membranous canal and ampulla; 3, 

 external or horizontal canal entirely opened ; 4, superior canal ; 5, utriculus or common 

 sinus with its group of otoliths ; 6, saccule with its otoliths ; 7, placed on the lamina 

 spiralis in the commencement of the scala vestibuli ; 7', scala tyrapani ; 8, membranous 

 ampulla of the superior semicircular canal ; 9, ampulla of the horizontal, and 10, that 

 of the posterior semicircular canal. 



B, membranous labyrinth and nervous twigs detached ; 1, facial nerve in the meatus 

 auditorius internus ; 2, anterior division of the auditory nerve giving branches to 5, 8, 

 and 9, the utricle and the ampullae of the superior and external canals ; 3, posterior 

 division of the auditory nerve, giving branches to the saccule ; 6, posterior ampulla, 10, 

 and cochlea, 4 ; 7, the united part of the superior and posterior canals ; 11, the posterior 

 extremity of the external canal. 



SEMICIRCULAR CANALS. The membranous semicircular canals are about 

 one third the diameter of the osseous tubes in which they are lodged, and 

 are dilated into ampullae within the ampullary enlargements of those tubes. 

 At the ampullae they are thicker and less translucent than in the rest of 

 their extent, and nearly fill their bony cases. That part of each ampulla 

 which is towards the concavity of the semicircle of the canal is free ; whilst 

 the opposite portion is flattened, receives branches of nerves and blood- 

 vessels, and presents on its inner surface a transverse projection, septum 

 transversum, which partly divides the cavity into two. The ampullae like- 

 wise contain otoliths in their epithelial lib ing. 



Auditory nerve: vestibular division. At the bottom of the meatus audi- 

 torius internus the auditory nerve divides into an anterior and a posterior 

 branch, which, broken up into minute filaments, pass through the perfora- 

 tions of the cribriform plate which separates the meatus from the internal 

 ear, and are distributed respectively to the cochlea and vestibule. In both 

 branches, as well as in the trunk, there are numerous nerve-cells, appa- 

 rently both with and without poles. The vestibular nerve divides into five 

 branches, which proceed respectively to the utricle, the saccule, and the 

 three ampullse of the semicircular canals : those for the utricle and the 



