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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. 23). 



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. Examination, however, of a 

 series of Weigert sections enables us to do this without 

 much difiiculty. 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 lies in the fioor of the fourth 

 ventricle, and the fibres pass right through the Gasserian 

 ganglion first into the Truncus infraorbitalis {t.inf.) and 

 then into the R. Mandibularis V {man. v.). On account 



