588 THE ORGANS 



brane also extends out as a cuticula over the cells of Hensen and of 

 Claudius. 



The Memhrana Tcctorla. — This is a peculiar membranous struc- 

 ture attached to a projection of the bony spiral lamina known as the 

 spiral lifubus (Fig. 390), the concavity beneath its attachment being 

 the internal spiral sulcus (Fig. 390, c). The membrane is non-nucle- 

 ated and shows line radial striations. It bridges over the internal 

 spiral sulcus and ends in a thin margin, which rests upon Corti's 

 organ just at the outer limit of the outer hair cells. 



Blood-vessels. — The arteries consist of two small branches of the 

 auditory — one to the bony labyrinth, the other to the membranous 

 labyrinth. The latter divides into two branches — a vestibular and a 

 cochlear. The vestibular artery accompanies the branches of the 

 auditory nerve to the utricle, saccule, and semicircular canals. It 

 supplies these parts, giving rise to a capillary network, w^hich is 

 coarse meshed except in the cristse and maculae, where the meshes are 

 fine. The cochlear artery also starts out in company with the audi- 

 tory nerve, but accompanies it only to the first tarn of the cochlea. 

 Here it enters the modiolus where it gives off several much coiled 

 branches, the glomerular arteries of the cochlea. Branches from 

 these pierce the vestibular part of the osseous spiral lamina and 

 supply the various structures of the cochlear duct. The veins ac- 

 company the arteries, but reach the axis of the modiolus through 

 foramina in the tympanic part of the bony spiral lamina. 



Lymphatics. — The scala media contains endolymph and is in 

 communication with the subdural lymph spaces by means of the en- 

 dolymphatic duct, the endolymphatic sac, and minute lymph chan- 

 nels connecting the latter with the subdural spaces. The perilymph 

 spaces — scala tympani and scala vestibuli — are connected with the 

 pial lymph spaces by means of the perilymphatic duct. Lymph 

 spaces also surround the vessels and nerves. These empty into the 

 pial lymphatics. 



Nerves. — The vestibular branch of the auditory nerve divides 

 into branches which supply the saccule, utricle, and semicircular 

 canals, where they end in the maculae and cristas as described on 

 page 581. The ganglion of the vestibular branch is situated in the 

 internal auditory meatus. The cochlear branch of the auditory 

 nerve enters the axis of the modiolus, where it divides into a number 

 of branches which pass up through its central axis. From these. 



