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line and not far from the ventral surface of the brain. 
Soon after leaving the brain the abducens passes sharply 
downwards to reach the floor of the brain case. In front 
it passes downwards and forwards, perforates the meninges, 
enters the eye muscle canal, and at once reaches the 
rectus externus muscle which it supplies. The abducens 
is the most posterior of the eye muscle nerves (cp. chart), 
and on this account the two nerves exhibit practically no 
traces of asymmetry. 
Before we can proceed to describe the trigeminal and 
facial nerves separately, it is necessary to interpolate an 
account of the roots and ganglia of the trigemino-facial 
complex as a whole (fig. 25). 
As in Teleosts generally the fifth and seventh nerves 
at their exit from the brain, and also their ganglia, are 
so disposed that it is quite impossible to completely 
analyse them by dissection. Hxamination, however, of a 
series of Weigert sections enables us to do this without 
much difficulty. Macroscopically there are two roots to 
the facial nerve and one to the trigeminal, and three of the 
four ganglia of these two nerves are compacted together 
into one mass. Analysis by serial sections reveals the 
following facts :— 
The most anterior root of the complex (r.v.) is that of 
the trigeminus. It lies, however, largely internal to and 
below the second root, so that it is at first not obvious on 
dissection, and emerges from the brain just below the 
cerebellum. It is the only root of the trigeminus, and 
consists of a general cutaneous and a motor component. 
The nucleus of the latter les in the floor of the fourth 
ventricle, and the fibres pass right through the Gasserian 
ganglion first into the Truncus infraorbitalis (t2nf.) and 
then into the R. Mandibularis V (man. v.). On account 
