THE INTERNAL EAR. 225 



Rings and Phalanges,'*- are very minute structures which connect the 

 ciliae of the hair-cells together, and form the Lamina Reticularis. (See 

 page 224.) 



Describe the Origin, Course and Distribution of the Auditory 

 Nerve. The 8th Cranial Nerve, or Portio Mollis of the 7th pair, arises by 

 two roots from the medulla oblongata, one from the floor of the 4th ventricle, 

 the other from a nucleus in the processus e cerebello ad medullam. It winds 

 around the restiform body, from which it receives fibres, and emerges at the 

 lower border of the pons, in company with the facial nerve. The two nerves 

 pass into the internal auditory canal, at the bottom of which the auditory nerve 

 divides into two branches, the vestibular and cochlear nerves. The 



Vestibular Nerve, has a ganglionic swelling on it in the internal auditory 

 canal, and then divides into 3 branches, which pass through the maculae 

 cribosae, and are distributed to the utricle, saccule, and the ampullae of the 

 semicircular canals, respectively. 



Cochlear Nerve, gives off a small branch to the wall between the utricle 

 and saccule, and then divides into numerous filaments which pass through 

 the small canals into the modiolus, to form a plexus between the two 

 plates of the lamina spiralis, from which filaments pass through the lower 

 edge of the lamina to terminate in the spindle-shaped cells of the organ 

 of Corti. (See page 224.) 

 Intumescentia Ganglioniformis Scarpa, is the ganglionic swelling on the 



vestibular nerve in the internal auditory canal. 



Ganglion Spirale, is a ganglion found on each filament of the cochlear 

 nerve, just as it enters between the plates of the lamina spiralis. 



What Arteries supply the Labyrinth ? The 



Internal Auditory Artery, br, of the basilar (from the vertebral), accom- 

 panies the auditory nerve into the internal auditory canal, where it divides 

 into vestibular and cochlear branches. 



Sty lo-mastoid Artery, br. of the posterior auricular (from the external carotid), 

 sends some small branches to the internal ear. 



Describe the Internal Auditory Canal. It begins by a large orifice on 

 the posterior surface of the petrous portion of the temporal bone, and runs 

 outwards for ^ inch, to end in a blind fossa, the floor of which is marked by 

 4 depressions, which are perforated by fine foramina, for the passage of the 

 filaments of the auditory nerve to the labyrinth. One of these depressions is 

 the 



Tractus Spiralis Forminosus, a spiral shaped depression containing a 

 number of the above foramina, situated opposi the base of the cochlea. 



Macula Cribosce, are the other 3 depressions. 

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