708 ORGANS OF SENSE. 



man, 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 

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

 ganglion-cells with caudate prolongations. 



The vestibular nerve, the 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 calcareous matter, others radi- 

 ating 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, p;i>s 

 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 con- 

 tains ganglion cells; and from the margin of the osseous zone, branches of 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 fila- 

 ments which supply the apical portion of the lamina spiralis, are conducted to 

 this part through the tubulus centralis rnodioli. 



