CRANIAL NERVES 137 



gest that they play an important part in proprioception, and this is 

 supported by Hoagland's experiments. 



The VIII nerve of Amblystoma carries fibers from the mem- 

 branous labyrinth, the structure of which resembles those of fishes 

 plus a recognizable rudiment of the cochlea. These fibers enter the 

 brain by two closely associated roots, dorsal and ventral, each of 

 which contains many rather fine myelinated fibers, with some very 

 coarse fibers mingled with them. Each fiber has a T-form division 

 within the brain, the branches ascending and descending through the 

 entire length of the medulla oblongata (figs. 7, 87-90). The dorsal 

 and ventral roots remain separate as far forward as the V root and 

 backward as far as the second root of the vagus. Beyond these limits 

 the two roots merge. It is evident that fibers of the ventral fascicle 

 take longer courses within the brain than do those of the dorsal 

 fascicle, but the significance of the separation of vestibular fibers 

 into two roots has not been determined. Some of these fibers descend 

 for a long and undetermined distance into the spinal cord, mingled 

 with the more ventral fibers of the dorsal funiculus and those of cor- 

 relation tract b. The ascending fibers enter the auricle (figs. 29, 30, 

 31, 91), where many of them end. Others continue into the body of 

 the cerebellum, decussate in the vestibulo-lateral cerebellar commis- 

 sure, and terminate in the vestibular and lateralis neuropil of the 

 auricle of the opposite side (figs. 32, 33, 34). 



Within the medulla oblongata the collaterals and terminals of the 

 vestibular fibers arborize in the common pool of neuropil, which also 

 receives terminals of the V and lateral-line roots. Most of the neurons 

 of the second order in the acousticolateral area spread their dendrites 

 within this neuropil so as to engage terminals of several of these 

 fascicles of root fibers of different physiological nature (fig. 9). 



There is ample physiological evidence that salamanders exhibit 

 vestibular control of posture and movement similar to that of other 

 animals, and this implies that there is some central apparatus that is 

 selective for the specialized end-organs of the internal ear. Sperry 

 ('45a) has shown that in the case of the frog this specificity is. pre- 

 served after section of the VIII nerve and its subsequent regeneration 

 and that the precision of restoration of vestibular function is quite as 

 exact as it has been shown to be in the case of regeneration of the 

 optic nerve (p. 229). Since the specific functions of the several 



