418 



PHYSIOLOGY 



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. 



Supr. cer. peduncle 



Kt. of 5th n. 



Valve of Vieussens 



Floor of 4th 

 ventricle 



Postr. long, 

 bundle 



Motor nucleus of 5th n. 



Motor root of 5th n. 



Sensory nucleus of 5th n.- 

 Supr. olive 



Sensory root 

 of 5th n. 



Middlcpedunclo 

 of cerebellum 



'~-^r sgiy Form, reticularis 



; x ,..y;v- 





FIG. 186. Transverse section through middh" of pons Varolii of orang on level of 



nuclei of fifth nerve. (CUNNINGHAM.) 



4 



A little further forward a section will escape the cerebellum alto- 

 gether, 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 forrnatio reticularis. They are 

 made up of fibres which run from the dentate nucleus of grey matter 

 in the cerebellum to the mid-brain, where they decussate below the 

 Sylvian iter and end in the red nucleus and in the thalamus of the 

 opposite side. They also contain the continuation upwards of the 



