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TEXT-BOOK OF PHYSIOLOGY. 



portion. Dendritic processes from these cells pass peripherally into the 

 internal ear, where they terminate on epithelial cells situated on the inner 

 surface of the utricle and saccule and in the ampullae of the semicircular 

 canals. 



The common trunk of the auditory nerve, consisting of both cochlear 

 and vestibular divisions after emerging from the internal auditory meatus, 

 I0 passes backward, inward, and downward 



..''' as far as the lateral aspect of the pons 



where the two divisions again separate. 



The cochlear nerve, the external root, 

 passes to the outer side of the restiform 

 body and enters the ventral acoustic 

 nucleus and the lateral acoustic nucleus, 

 around the cells of which its end-tufts 

 arborize. The vestibular nerve, the in- 

 ternal root, passes on the inner side of 

 the restiform body to the dorsal portion 

 of the pons, where, after bifurcating, 

 the end-tufts of the axons arborize around 

 the dorso-internal or chief auditory nu- 

 cleus and the dorso-external or Deiters' 

 nucleus. Some of the fibers of the ves- 

 tibular branch descend through the pons 

 and medulla as far as the cuneate 

 nucleus. 



Cortical Connections. The coch- 

 lear nerve is ultimately connected with 

 the cerebral acoustic area, in the tem- 

 poral lobe of the opposite side through 

 the intermediation of the auditory tract. 

 This tract is complex and involved. 

 ^- n a g enera ^ wa Y & ma y ^e said to con- 



FIG. 279. ORIGIN AND TERMINATION 

 OF THE AUDITORY NERVE, i. Cochlea. 



nerve. 4. Ventral acoustic nucleus. 5. 

 Lateral acoustic nucleus. 6. Semi- 

 circular canals. 7. Ganglion of Scarpa. 

 8. Vestibular nerve. 9. Dorso-external 

 nucleus (Deiters). 10. Dorso-internal 

 nucleus. {After Moral and Doyon.} 



2. Spiral ganglion (Cord). 3. Cochlear sist in part of fibers which come direct 



from the cochlear branch. After pass- 

 ing through the ventral nucleus and the 

 trapezoid body they cross the median 

 line, enter the lemniscus or fillet, and 

 finally terminate in the pre- and post- 

 geminal bodies. In their course they give off collateral branches to these 

 various nuclei through which they pass. Other fibers taking their origin 

 from cells in these various nuclei proceed to the cortex where they terminate. 

 Properties. Stimulation of the cochlear nerve is unattended by either 

 motor or sensor phenomena. Division of the nerve is followed by a loss 

 of the sense of hearing. Irritative pathologic lesions give rise to sensations 

 of sound of varying character and intensity. Degeneration of the nerve or 

 destruction by tumors, etc., will also be followed by a loss of the sense of 

 hearing. 



Experimental lesions of the semicircular canals involving a destruction 

 of the physiologic relations of the vestibular nerve are followed by a loss of 



