THE MEDULLA OBLONGATA. 



145 



directions through the grey matter towards these cells, and evidently 

 communicate with them (Fig. loi j?;). One small group (Fig. loi r) 

 passes to a lower level than the rest, and is regarded by Stieda as 



Fig. loo. 



Transverse section through the Medulla oblongata at the point of origin of the abdiicens nerve, 

 from Stieda. Magnified 30x80.) 



h Fourth ventricle. 



m Abducens nerve. 



/( Auditory nucleus. 



o Abducens nucleus. 



the true auditory centre. Kcippen considers that the auditory nerve 

 has a threefold origin : (i) from small cells on the median surface 

 of the auditory area ; (2) from the large cells between the above ; 

 (3) from a group of free nuclei on the dorsal surface of the auditory 

 area. 



3. The trigeminal nucleus {nudetis trigemmiis), (Fig. loi q) 

 lies in part beneath the auditory nucleus but extends further 

 forwards. It forms a rounded group of cells placed under the outer 

 angle of the grey matter. The cells are somewhat crowded together, 

 and are chiefly of an elongated spindle-form, ^àth their processes 

 directed obliquely downwards and outwards. The fibres of the trige- 

 minal nerve sej)arate into two groups ; the upper group is best traced 

 in a horizontal section, the fibres curving round to join the longitu- 

 dinal fibres continued from the dorsal columns of the cord. The 

 fibres of the lower, smaller group pass transversely inwards to the 



