1522 



HUMAN ANATOMY. 



spiral canal and collectively constitute the ganglion spirale. From these cells 

 numerous dendrites are given off, which pass along the canals within the spiral 

 lamina towards its margin, the twigs meanwhile subdividing to form an extensive 

 plexus contained within corresponding channels in the bone. At the edge of the 

 spiral lamina bundles of fine fibres are given off, which escape at the foramina nervosa 

 of the labium tympanicum and enter the epithelial layer close to the inner rod of Corti. 

 During or before their passage through the foramina, the nerve-fibres lose their med- 

 ullary substance and proceed to their destination as fine naked axis-cylinders. The 

 radiating bundles pass within the epithelium to the mesial side of the base of the inner 

 pillar ; here they divide into two sets of fibrillae, one, the mesial spiral fasciculus, 

 going to the inner hair-cells and the other, the lateral spiral fasciculus, passing 

 between the inner pillars to reach the tunnel of Corti. Within this space fibrillae are 

 given off which, after crossing the tunnel, escape between the outer rods into the 

 epithelium lying on the lateral side of the arch. The further course of the fibrillae 

 seems to be such that some extend between the outer pillar of Corti and the first rows 

 of hair-cells, whilst succeeding groups of fibrillae course between the rows of Deiters' 



FIG. 1275. 



.-= \& 1- /^\ 

 =i h 5JS If 5| 



uperior canal 



Ductus endolymphaticus 



Ligamentum 

 spirale ""* 



Basilar^ 

 membrane 



Branches of cochlear nerve to \ Posterior canal 



Corti's organ Membranous cochlea | Blind sac of ductus cochlearis 



Canalis reuniens opening into cochlear duct Branch of vestibular nerve to posterior canal 



Membranous labyrinth of five months foetus, postero-mesial aspect ; u, utricle ; ss, sf>, superior and posterior utric- 

 ular sinus; j, saccule; us, utriculo-saccular canal ; cr, canalis reuniens; pa, posterior ampulla. X 6. (Ketzius). 



cells to reach the remaining hair-cells. The relation between the nerve-fibrils and 

 the auditory cells is in all cases probably close contact and not actual junction with 

 the percipient elements. The paths by which the impulses collected from the audi- 

 tory cells are conveyed to the cochlear nucleus, and thence to the higher centres, are 

 described in connection with the Auditory Nerve (page 1258). 



Blood- Vessels of the Membranous Labyrinth. The arteries supplying 

 the internal ear arise from the internal auditory artery, supplemented to a limited 

 extent by branches from the stylo-mastoid. The auditory artery, a branch of the 

 basilar, after entering the internal auditory meatus divides, according to Siebenmann, 

 into three branches : (i) the anterior vestibular, (2) the cochlear proper, and (3) 

 the vestibuh-cochlmr <///<;). 



i. The vestibular artery accompanies the utriculo-ampullary nerve and sup- 

 plies the upper part of the vestibule, including the posterior part of the utricle with 

 it> inacul.i. th. s.iccule and the cristae of the upper and outer ampullae of the corre- 

 sponding semicircular canals. 



Hie cochlear artery pursues a spiral course. It gives off three branches, 

 two ,,f which are distributed t.) the lower turn of the cochlea, whilst the third sup- 

 plie^ the middle and apical turns. 



The vestibulo-cochlear artery arises either from the cochlear artery or 

 independently and divides, within the spiral lamina, into a cochlear and a vestibular 





