AUDITORY BLOODVESSELS AND NERVES. 687 



saccule. Within the enlargement of each semicircular tube there is also 

 a calcareous material. 



BLOODVESSELS. The membranes of the labyrinthic cavity receive 

 their blood from an artery which enters the internal auditory meatus with 

 the nerve ; but some offsets from the posterior auricular supply their 

 hinder part. 



The internal auditory artery arises from the basilar trunk within the 

 skull (p. 175), and enters the internal meatus with the auditory nerve. 

 In the bottom of that hollow it divides into two branches one for the 

 vestibule, the other for the cochlea. 



The branch of the vestibule, after piercing the wall of the cavity, sub- 

 divides into small offsets, which supply the lining membrane, and ramify 

 over the sacs, and the tubes occupying the semicircular canals. The 

 vessels end in a network of capillaries on the exterior of the special 

 layer of the sacs, and this is most developed about the termination of the 

 nerves. 



The branch of the cochlea subdivides into twigs which enter the canals 

 in the modiolus. Small offsets from these are directed outwards through 

 canals in the lamina spiralis, and communicate together in loops near the 

 margin of that osseous zone. From this anastomosis vessels are supplied 

 to the basement layer and the membrane lining the scalae ; but the 

 septum cochleae prevents the communication of the vessels of the two 

 passages. 



A longitudinal vessel is placed on that surface of the membranous part 

 of the septum cochleae which is turned to the scala tympani, and is oppo- 

 site the outer rods of Corti ; it communicates here and there with the 

 arterial loops before mentioned. 



The vein. One branch of vein is derived from the cochlea, and 

 another from the membranous labyrinth : the two are united near the 

 cochlea, and the trunk ends in the superior petrosal sinus in the base of 

 the skull. 



NERVE OF THE LABYRINTH (fig. 249). Only one special nerve, audi- 

 tory (p. 181), is distributed to the labyrinth. Entering the internal 

 auditory meatus, the nerve divides into two branches, like the artery, 

 viz., an anterior for the cochlea, and a posterior for the membranous 

 labyrinth. In the trunk and in both branches nerve cells are contained : 

 in the branch to the labyrinth they form a swelling (intumescentia ganylio- 

 formis of Scarpa). 



The cochlear branch divides at the base of the modiolus into twigs, 

 which enter it, and are directed outwards with the vessels into the canals 

 in the lamina spiralis (fig. 247, "). As they enter the lamina they form 

 a plexus with ganglion cells, and are continued onwards near the scala 

 tympani, being still plexiform, as far as the edge of the bone. At this 

 spot they leave the bone, and are arranged in conical bundles, which pass 

 through apertures at the junction of the bone with the lamina basilaris of 

 the septum cochleae : consisting now of axis cylinders they are directed 

 towards the cells of the organ of Corti, but their ending is unknown. 



The vestibular branch ends in three nerves for the membranous laby- 

 rinth ; these pierce the cribriform plate in the bottom of the meatus, and 

 are thus distributed : One appertains to the utricle (e), and to the en- 

 largements on the tubes contained in the superior vertical and horizontal 

 semicircular canals (fig. 249) ; a second ends in the saccule (a) ; and the third 



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