260 PRACTICAL HISTOLOGY [XXXII 



The anterior column tracts, now called the posterior longitudinal 

 bundles, are almost immediately beneath the floor of the ventricle; 

 laterally of the p. 1. b. is a marked round bundle, the root of the 7th 

 nerve ; ventro-laterally of this is the nucleus of the 6th nerve. Some 

 root fibres of the 6th may be seen a little medially of the upper olive. 



In a section taken a little more anteriorly the fibres of the 7th n. 

 will be seen running out between the bulbar 5th and the upper olive. 



10. Section through the motor nucleus of the 5th nerve. 



The pons is large occupying to of the dorso- ventral diameter. 

 The fillet is more elongated, is farther from the raphe, and 

 stretches a little up the lateral surface of the reticular area ; 

 there may be a small piece of the upper olive ; trapezium fibres 

 are present in the lower sections \ on the dorso-lateral boundary 

 of the ventricle is a large comma-shaped mass of fibres (seen 

 with the eye) the superior cerebellar peduncle (it arises chiefly 

 from the dentate nucleus). The large lateral masses of white 

 substance are part of the middle peduncles of the pons. 



Note : 



The bulbar 5th fibres running obliquely outwards but not 

 yet at the surface. A band of fibres (chiefly of the motor and 

 mid-brain roots) extending dorsally and medially of the bulbar 

 5th. 



Medially of this a group of large nerve cells the motor 

 nucleus of the 5th nerve, and laterally of it, one or more 

 clumps of grey substance without obvious nerve cells the 

 sensory nucleus of the 5th nerve. 



In the ventral part of the grey substance of the 4th ventricle, 

 curving fibres running to the band between the sensory and motor 

 nucleus. 



Just beneath the grey substance of the floor of the 4th 

 ventricle, on either side of the raphe, a triangular bundle of 

 large fibres the posterior longitudinal bundle. A bundle in 

 this position more or less marked off from the rest can be seen 

 in several of the sections already examined. 



