THE CRANIAL NERVES. 549 



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 internal 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 nucleus and the dorso- external 

 or Deiters' nucleus. Some of the fibers of the vestibular branch 

 descend through the pons and medulla as far as the cuneate nucleus. 



Cortical Connections. The cochlear nerve is ultimately con- 

 nected with the cerebral acoustic area, in the temporal lobe of the 

 opposite side through the intermediation of the auditory tract. This 

 tract is complex and involved. In a general way it may be said to 

 consist in part of fibers which come direct from the cochlear branch. 

 After passing 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 fol- 

 lowed 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 the coordinating and equilibratory power. 

 Disordered movements, such as rotation to the right or left, somer- 

 saults backward and forward, follow destruction of these canals. 

 Pathologic lesions in the peripheral distribution of the nerve are 

 attended in man by disturbances of equilibrium; e. g., vertigo, a sense 

 of swaying, pitching, and staggering. 



Functions. The function of the cochlear nerve is to convey 

 nerve impulses from its origin to the pons, from which they are 

 transmitted by the auditory tract to the acoustic area in the cerebral 

 cortex. The specific physiologic stimulus to the development of 

 these impulses is the impact of atmospheric undulations on the tym- 

 panic membrane, received and transmitted by the chain of bones 

 to the structures of the internal ear, the organ of Corti, with which 

 the peripheral terminations of the nerve are connected. The function 

 of the vestibular nerve is the transmission of nerve impulses to the 



