356 C. JUDSON HERRICK 



most dorsal part of the white substance. This area was seen in 

 Necturus by Kingsbury ('95, p. 187), who termed it the dorsal 

 island of alba, and by Norris in Amphiuma ('08, p. 536) and in 

 Siren ('13, p. 283), by whom it was compared with the lobus 

 lineae lateralis of fishes. This 'dorsal island,' in both the 17 mm. 

 and the 38 mm. larva, receives fibers only from the dorsal lateralis 

 VII root, so far as I have observed, and its position is not marked 

 by an external eminence. In the adult, however, it is much 

 enlarged, and with the associated part of the stratum griseum, it 

 completely fills a large eminence bordering the tenia of the fourth 

 ventricle. In the adult, moreover, it receives large fiber bundles 

 from the middle and ventral lateralis VII roots within the white 

 substance of the oblongata. The entire structure in the adult 

 much more strongly resembles the lobus lineae lateralis of the 

 generalized fishes than in the young larva or the adults of the lower 

 urodeles described by Kingsbury and Norris. 



In the 38 mm. larva the ascending and descending branches of 

 the dorsal lateralis VII root fibers extend only a short distance 

 before terminating in the associated neuropil, their rostral limit 

 being at the level of the V roots and their caudal limit at the level 

 of the IX roots. The fibers of all of the other sensory roots 

 which enter the oblongata extend much farther both rostrad and 

 caudad. 



The dorsal lateralis VII root of this description is evidently the 

 same as the root VII b^ of Strong ('95) and Kingsbury ('95). The 

 root VII b- of these authors includes my middle and ventral lat- 

 eralis VII roots. 



Since the fibers of the dorsal lateralis VII root are smaller 

 than any others of this system in these young larvae (this is not 

 true in the adult), their peripheral course can be followed with ease. 

 When this root is followed peripheralward from the oblongata, 

 some of its fibers are seen to turn directly ventralward to enter the 

 hyomandibular trunk for the ramus mentalis VII (the urodele 

 equivalent of the teleostean r. mandibularis externus VII); 

 but clearly in these larvae most of the fibers of this root enter the 

 anterior division of the lateralis VII root complex to distribute in 

 both the ramus ophthalmicus superficialis VII and the ramus 



