104 GEORGE W. BARTELMEZ 
said (p. 94) that the superior ventral dendrite branches in the 
dendritic field of the pars premauthnerea nuclei motorii tegmenti . 
and the inferior dendrite has the same relation to the pars post- 
mauthnerea. Accordingly what is said of these ventral dendrites _ 
holds also for the associated groups of the tegmental nucleus. 
The superior dendrite is characterized by its close relation to the 
nucleus princeps V. At no other level are the fine fibers which 
stream ventrally into the ventro-lateral neuropil of the same 
side so abundant as in the region of the pars premauthnerea, 
especially its caudal end where the superior dendrite ramifies. 
The fibers of the indirect cerebello-tegmental system can also be 
traced into this region but not farther caudally (p. 95). More- 
over, it is obvious from what has been said of the position of the 
ventral acoustic nuclei in Ameiurus that in this form the superior 
dendrite is rostral to any part of these nuclei and it has no obvious 
connection with them as it has in Salmo. The inferior ventral 
dendrite, on the other hand, and its associated group (pars post- 
mauthnerea) are intimately related to the ventral acoustic nuclei. 
~ I would suggest the following as a reason for the phylogenetic 
development of the inferior ventral dendrite of Ameiurus: when 
in the hypertrophy of the gustatory system the ventral acoustic 
nuclei were crowded caudally and so separated from Mauthner’s 
cell, the superior ventral dendrite retained its position because 
of its intimate relation to the chief Vth nucleus and cerebellum, 
while the inferior dendrite was developed to receive the impulses 
from the ventral VIIIth nuclei. The ventro-lateral neuropil is 
more dense in the region where these two dendrites and their 
associated cells branch than at any other level. That is because 
the collaterals from the long tracts, namely the tecto-bulbar sys- 
tem, the fasciculi longitudinales medialis et lateralis and from 
the acoustico-lateral decussation which reach all other parts of 
the nucleus motorius tegmenti are most abundant at this level. 
The chief impulses, then, which reach Mauthner’s cell by way 
of its ventral dendrites come from the ventral acoustic nucleus, 
from the chief Vth nucleus, from the tectum through the crossed 
and uncrossed tecto-bulbar tracts and from the cerebellum by 
way of the indirect cerebello-tegmental system. 
