AUDITORY ORGAN. XI:} 



Into the organ of Corti the ramus cochlearis of the n. acusti- 

 cus sends its end ramifications. It passes up in the axis of the 

 cochlea and gives off branches which run toward the lamina 

 spiralis ossea. Here at its base the cochlear nerve possesses a 

 ganglion which follows the spiral windings of the cochlea, and 

 is therefore known as the ganglion spirale. Each rnedullated 

 nerve fibre passes over into a bipolar ganglion cell. The sec- 

 ond process originating in the opposite pole of the cell becomes 

 a medullated fibre. This enters the lamina spiralis ossea, and 

 takes part in the formation of a nervous plexus. In passing 

 through the foramina nervina these -fibres lose their medullary 

 sheaths and enter the organ of Corti as naked axis cylinders. 

 Here they lie in many bundles, which in part run spirally in 

 the cochlea, and in part proceed directly to the bases of the 

 inner and outer hair cells, passing through the canal of Corti 

 and the space of Nuel. The terminal branches of the fibres 

 surround the lower parts of the hair cells and end on their sur- 

 face. These cells are sense cells, which take up auditory im- 

 pressions and pass them on to the first peripheral neurones, 

 whose cell bodies lie in the ganglion spirale. 



(3) Blood-vessels of the Membranous Labyrinth. 



The branch of the arteria auditiva which supplies the mem- 

 branous labyrinth breaks up into three twigs, namely, the art. 

 vestibularis, the art. cochlearis, and the art. vestibulocochlearis 

 (Siebenmenn). 



(a) The arteria vestibularis supplies the n. vestibularis, the 

 upper and lateral parts of the sacculus and utriculus, and the 

 ampullae of the upper and lateral semicircular canals. 



(b) The arteria vestibulocochlearis supplies, by its vestibular 

 branch, the lower median half of the sacculus and utriculus, the 

 posterior ampulla, the lower end of the cochlea; and by its 

 cochlear branch the first third of the first coil of the cochlea. 



(c) The rest of the cochlea is supplied with blood by the 

 arteria cochlearis. This breaks up in the axis of the cochlea 

 into three or four branches, which run spirally and give off 

 numerous twigs in a radial direction. Some of these are for the 



