THE EAR 



'55* 



lamina cribrosa at the deep end of the internal meatus. They are 

 distributed to the macula acustica utriculi and to the cristae acusticae 

 of the ampullae of the superior and external semicircular canals. 



The cochlear nerve, in the meatus auditorius intemus, furnishes 

 two branches — one to the macula acustica sacculi, and the other to 

 the crista acustica of the ampulla of the posterior semicircular 

 canal. The filaments of the former, which has a gangliform en- 

 largement, pass through the foramina in the inferior vestibular area 

 of the lamina cribrosa, and the latter passes through the foramen 

 singulare in the lamina cribrosa. The cochlear nerve, having 

 parted with these two branches, breaks up into filaments which 

 pass through the foramina of the cochlear area of the lamina 

 cribrosa, and so reach the base of the modiolus of the cochlea. 

 They traverse the canals of the modiolus, from which they pass 

 into the canals between the two layers of the lamina spiralis. In 

 doing so they have to cross the spiral canal of the modiolus, which 



, Helicotrema 



Scala Ve&tibuU 



Membranous Spiral 

 Lamina 



Scala Tympani 



Expansion of Cochlear Nerve 



Fig. 655. — Section of the Cochlea, showing the Distribution of the 

 Cochlear Branch of the Auditory Nerve (magnified) (Hirschfeld 



AND LeVEILLE). 



is situated close to the attached margin of the lamina spiralis. This 

 canal contains a ganglion, called the spiral ganglion, which pursues 

 the windings of the canal, and consists of bipolar nerve-cells. As 

 the auditory fibres pass from the canals of the modiolus into the 

 canals of the lamina spiralis, the course of each fibre is probably 

 interrupted by a bipolar cell of the spiral ganglion in the spiral 

 canal. The nerve-fibres, having emerged from these bipolar cells, 

 traverse the canals between the two layers of the lamina spiralis. 

 Having lost their medullary sheaths, they emerge through the 

 foramina of the labium tympanicum on the outer margin of the 

 limbus laminae spiralis, and enter the basilary membrane, where 

 they terminate in arborizations which are connected with the inner 

 and outer hair-cells. 



Blood-supply ot the Labyrinth. — The labyrinth derives its blood 

 from the internal auditory artery, which is a branch of the basilar 

 artery. The vessel traverses the meatus auditorius intemus, and 



