MEDULLA OBLONGATA OF AMBLYSTOMA 359 



lateralis, and some of their ascending fibers reach to the extreme 

 rostral end of the auricular lobe, where they end in intimate 

 association with those of the medial and ventral lateralis VII 

 roots. Between the V and VII roots many fibers of the ventral 

 lateralis X root are seen in horizontal sections to turn and enter 

 fascicles of arcuate fibers. They cross to the opposite side of the 

 oblongata and their farther course is unknown. 



The roots of the VIII nerve. The fibers of this nerve enter the 

 oblongata by two imperfectly separated roots (dorsal and ventral) 

 each containing fine fibers with some very coarse ones mingled 

 with them. Peripherally also the coarse and fine fibers seem to be 

 mingled in the various rami, but no attempt has been made to 

 determine their distribution. The VIII ganglion is made up of 

 very small cells, with some of medium size, all of which are bipolar. 

 The two VIIT roots enter the brain dorsally of the spinal V root 

 and chiefly ventrally of the visceral sensory VII root, though some 

 fibers of the dorsal root enter above the visceral sensory root 



(fig. 12). 



The fibers of both roots divide immediately within the oblon- 

 gata (fig. 48) and two fascicles of VIII root fibers may be distin- 

 guished for a long distance cephalad and caudad of the superficial 

 origin of the nerve, derived respectively from the dorsal and ven- 

 tral VIII roots. The fibers of the ventral fascicle run a longer 

 course within the brain than do those of the dorsal fascicle. 

 Mauthner's cell lies at the entrance of the VIII roots and two 

 of its chief dendrites pass outward among the entering root fibers 

 quite to the surface of the oblongata, one above and the other 

 below the visceral sensory VII root (figs. 12, 53). 



The dorsal and ventral ascending tracts of VIII root fibers 

 remain distinct as far forward as the superficial origin of the V 

 roots, beyond which they can no longer be separated. The 

 combined root, of rather fine fibers, can readily be followed to the 

 extreme rostral end of the auricular lobe, where, much reduced in 

 size, it turns abruptly dorsalward (fig. 6) to terminate in the ven- 

 tral part of the body of the cerebellum. A residue of the lateralis 

 VII roots can be followed almost as far dorsally as these VIII 

 fibers, ending in the same vicinity farther laterally. 



THE JOURNAt. OS COMPARATIVE NEUROLOGY, VOL. 24, XO. 4 



