THE STRUCTURE OF THE BRAIN STEM ,7, 



in the outer part of the formatio reticularis are the representative of t 

 lateral columns of the cord after the removal of the direct cerebellar and tl 

 crossed pyramidal tracts. They include therefore the antero-lateral ascend 

 ing tract (tract of Gowers) and a number of other fibres corresponding to the 



Supr. cer. peduncle 



Kt. of 5th n 



Motor nucleus of 5th n 



Motor root of 5th n 



Sensory nucleus of 5th n. 

 Supr. olive 



Sensory root 

 of 5th n. 



Middle peduncle 

 of cerebellum 



Valve of VieuBueng 



Floor of 4th 

 ventricle 



Postr. long, 

 bundle 



Form.reticularifc 



Corpus 

 trapczoidctt 



FIG. 185. 



Transverse section through middle of pons Varolii of orang on level of 

 nuclei of fifth nerve. (CUNNINGHAM.) 



lateral basis bundle in the cord. In the mesial part of the formatio reticu- 

 laris the longitudinal tracts are the tract of the fillet and the posterior longi- 

 tudinal bundle on each side of the middle line. In the upper part of the pons 

 Varolii a well-marked collection of transverse fibres are to be seen lying 

 dorsally to the tracts of the fillet. This collection is called the corpus 

 trapezoides and is made up of ascending fibres derived from the nuclei of the 

 cochlear nerve, the auditory part of the eighth nerve. 



A little further forward a section will escape the cerebellum altogether, 

 being bounded ventrally by the upper or anterior part -of the pons and 

 dorsally by a thin mass of grey matter, the valve of Vieussens (Fig. 186). 

 On each side of the valve of Vieussens may be seen the superior peduncles of 

 the cerebellum. As these peduncles are traced upwards they sink gradually 

 deeper into the pons until they lie on the outer side of the tegmental region 

 or formatio reticularis. They are made up of fibres which run from the 



