MAUTHNER’S CELL 101 
dendrite (S.Vent.Dend.). The former extends almost to the lat- 
eral periphery of the oblongata branching among the VIIIth 
root fibers and the cells of Deiters’ nucleus. The ventral one 
extends somewhat rostrally and branches widely in the neuropil 
formed by collaterals from the tracts of the ventro-lateral col- 
umns and by the dendrites of the pre-mauthnerean group of the 
nucleus motorius tegmenti (fig. 2). It is interesting to note that 
the girth of these large dendrites is relatively greater in larvae 
than in adults, as may be judged from figures 6 and 11. In addi- 
tion to these two, Beccari describes.in Salmo a medium-sized 
dendrite branching in the fasciculus longitudinalis medialis (Med.. 
Dend. of fig. 6). This is almost always present and fairly con- 
stant in its relations. The small ventral dendrites related pri-- 
marily to the fasciculus longitudinalis lateralis (Mayser ’82) are 
more variable in number and position and are apparently more 
numerous, certainly more obvious, in the larva than in the adult. 
There is another type of dendrite, less conspicuous than the 
others, which has hitherto escaped notice. These arise from the: 
region of the axone hillock; two of them are labelled C.Dend. in 
figure 11. It must be remembered that all of these dendrites do 
not lie in a single plane, but are so projected in figures 3, 6 
and 11. 
The dendrites will now be considered in more detail with espe- 
cial reference to their appearance in Ameiurus. 
Lateral dendrite. The lateral dendrite is theoretically the most 
significant, for it is almost exclusively related to the periphery, 
and this direct relation to the VIIIth root is the only fundamental 
character which distinguishes Mauthner’s cell from the other 
cells of the nucleus motorius tegmenti. According to Beccari 
(07) it has only terminal branches, but figure 6 shows other 
small ones in the trout; they may be seen in Ameiurus in figures 
3 and 10. The terminal branching was well figured by Bececari 
and figure 6 shows that the branching is confined to the region 
of Deiters’ nucleus. There is no evidence in any teleost of the 
large dorsal branch of the lateral dendrite which in urodeles 
ramifies in the dorsal acoustic nucleus (Beceari, ’07, Herrick, ’14). 
In other words, the impulses entering the lateral dendrite come 
