528 ; DAVIDSON BLACK 
at the rostral end of the nucleus. The nucleus is traversed by 
many thick bundles of the dorsal arcuate fibers. 
The motor VII fibers which arise from cells in the rostral end 
of the VII-IX—X column (caudal motor VII nucleus) pass up- 
wards through the medulla as a small compact bundle, situated 
just above the most dorsal fibers of the fasciculus longitudinalis 
medialis (fig. 30). At the level of the rostral motor VII nucleus, 
fibers from this center join the ascending root. In this way at the 
level of the upper border of the rostral motor VII nucleus, a 
large compact bundle is formed which derives its fibers from 
both rostral and caudal motor VII nuclei. The VII motor 
root then passes rostrad for some distance and finally curves 
outwards over the radix descendens V and reaches the lateral 
surface of the medulla some sections rostrad of the sensory VII 
root (fig. 31). 
In Ameiurus the motor VII nucleus consists of a large mass of 
cells situated in the tegmentum below the acoustic commissure, 
resting medially upon the fasciculus longitudinalis lateralis and 
laterally upon the reticular substance bordering the ascending 
secondary gustatory tract of Herrick. These relations are 
brought out in figure 32 and are essentially similar to those 
obtaining in Siluris glanis. A caudal motor VII nucleus, in 
continuity with the [IX—X motor column, is not present in either 
Silurus or Ameriurus, so that in these forms all the motor VII 
fibers arise in a nucleus corresponding to the rostral motor VII 
nucleus of Solea (fig. 41 A). ; 
The motor VII fibers collect to form a large compact bundle 
which arches dorsally over the massive acoustic commissure and 
courses rostrad in the ventricular gray. At the level of the 
caudal portion of the motor V nucleus, the root curves laterad 
through the bundles of dorsal arcuate fibers and pierces the sec- 
ondary gustatory tract to gain the lateral periphery of the 
bulb (fig. 33). 
Abducens nucleus and roots (Nu. et rad. N. VI). In Solea, in 
the ventral tegmentum, at the exit level of the motor VII root, a 
poorly circumscribed nucleus is found, from which arises the 
most rostral of the two abducens rootlets (fig. 31). The emer- 
