"3 JO PROCEEDINGS OP THE CANADIAN INSTITUTE. 



by the commissure/, accessories of Mau timer, and the extremely broad 

 ' fibres of Mauthner' are found in the upper compartments. At 

 either side of the central canal is the nucleus of one of the motor 

 roots of the second part of the vagus, and on either side of the ven- 

 tral longitudinal fibres the nucleus of the first spinal nerve. 



Fig. 2 represents a section passing through the anterior part of the 

 vagus lobes, and through the origin of the first part of the vagus. 

 Those fibres which join the nerve from the tuberculum acusticum are 

 cut transversely, and are seen above the eighth nerve in the next 

 figure. The sensory vagus fibres arise chiefly from the periphery of 

 the lobe, while fibres which originate near the wall of the fourth 

 ventricle collect themselves into a strong bundle, reinforced by simi- 

 larly originating fibres from the trigeminal lobe (Fig. 3) and are thence 

 to be traced forwards into the cerebellum as the secondary vago- 

 trigeminal tract of Mayser. {Sec. V. T.) This strong fasciculus lies 

 immediately below the ascending roots of the fifth nerve. The fourth 

 ventricle is slit-like in section, except where it becomes somewhat 

 wider above where its roof is formed only by ependyma and pia. 

 The slit-like section is retained except where encroached on by the 

 trigeminal lobes, until it becomes opened out immediately in front of 

 these (Fig. 4) to be closed again by the commissure of grey matter 

 which joins the tubercula acustica (Fig. 5). These ganglia are 

 further connected by fibres which decussate below the floor of the 

 fourth ventricle. (Figs. 3 and 4). 



From the various parts of the tuberculum fibres converge to form 

 the auditory nerve (iV. VII L), but it also receives a contingent from 

 a nucleus lying below the secondary vago-trigeminal fasciculus. 



The whole of the trigeminal lobe serves to give origin to the sen- 

 sory fibres of the fifth nerve which form the powerful ' dorsal genicu- 

 lated root,' trending outwards in Fig. 4. In the same plane the motor 

 fibres of the facialis (N~. VII.) escape, partly derived from a nucleus 

 represented in the figure, but largely composed of a strand which 

 stretches outwards, forwards and downwards from the floor of the 

 fourth ventricle. It may be recognized in transverse section in 

 Fig. 3, before it has begun to assume the course above named. 



Fig. 5 illustrates a section passing through the trigeminal roots. 

 The fibres derived from the tuberculum acusticum are most superficial, 

 the ascending and transverse fibres most anterior and ventral ; the 

 change of position which the latter undergo with regard to the dorsal 



