642 ORGANS OF THE SENSES. 



The endolymph (liquor Scarpse] is a limpid serous fluid, which fills the mem- 

 branous labyrinth ; in composition, it closely resembles the perilymph. 



The otoliths are two small rounded bodies, consisting of a mass of minute 

 crystalline grains of carbonate of lime, held together in a mesh of delicate fibrous 

 tissue, and contained in the wall of the utricle and saccule, opposite the distribu- 

 tion of the nerves. A calcareous material is also, according to Bowman, sparingly 

 scattered in the cells lining the ampulla of each semicircular canal. 



The Arteries of the labyrinth are the internal auditory from the basilar or 

 superior cerebellar, the stylo-mastoid from the posterior auricular, and, occasion- 

 ally, branches from the occipital. The internal auditory divides at the bottom of 

 the internal meatus into two branches, cochlear and vestibular. 



The cochlear branch subdivides into from twelve to fourteen twigs, which 

 traverse the canals in the modiolus, and are distributed, in the form of a capillary 

 network, in the substance of the lamina spiralis. 



The vestibular branches accompany the nerves, and are distributed, in the form 

 of a minute capillary network, in the substance of the membranous labyrinth. 



The Veins of the vestibule and semicircular canals accompany the arteries, and, 

 receiving those of the cochlea at the base of the modiolus, terminate in the superior 

 petrosal sinus. 



The Auditory nerve, the special nerve of the sense of hearing, divides, at the 

 bottom of the internal auditory meatus, into two branches, the cochlear and vesti- 

 bular. The trunk of the nerve, as well as the branches, contains numerous ganglion 

 cells with caudate prolongations. 



The Vestibular nerve, the most posterior of the two, divides into three branches, 

 superior, middle, and inferior. 



The superior vestibular branch, the largest, divides into numerous filaments, 

 which pass through minute openings at the upper and back part of the cul-de-sac 

 at the bottom of the meatus, and, entering the vestibule, are distributed to the 

 utricle, and to the ampulla of the external and superior semicircular canals. 



The middle vestibular branch consists of numerous filaments, which enter the 

 vestibule by a smaller cluster of foramina, placed below those above mentioned, 

 and which correspond to the bottom of the fovea hemispherica ; they are dis- 

 tributed to the saccule. 



The inferior and smallest branch passes backwards in a canal behind the 

 foramina for the nerves of the saccule, and is distributed to the ampulla of the 

 posterior semicircular canal. 



The nervous filaments enter the ampullary enlargement at a deep depression seen 

 on their external surface, and a corresponding elevation is seen within, the nerve 

 fibres ending in loops, and in free extremities. In the utricle and saccule, the 

 nerve fibres spread out, some blending with the calcareous matter, others radiat- 

 ing on the inner surface of the wall of each cavity, becoming blended with a layer 

 of nucleated cells, and terminating in a thin fibrous film. 



The Cochlear nerve divides into numerous filaments at the base of the modiolus, 

 which ascend along its canals, and then, bending outwards at right angles, pass 

 between the plates of the bony lamina spiralis, close to its tympanic surface. 

 Between the plates of the spiral lamina, the nerves form a plexus, which contains 

 ganglion cells ; and from the margin of the osseous zone, branches from this plexus 

 are distributed to the membranous part of the septum, where they are arranged in 

 small, conical-shaped bundles, parallel with one another. The filaments which 

 supply the apical portion of the lamina spiralis are conducted to this part through 

 the tubulus centralis modioli. 



