STRUCTURE OF THE PONS VAROLII 



197 



which is met with at the upper part of the medulla, but the general 

 appearance of the section is much modified by the presence of a 

 large number of transversely coursing bundles of nerve-fibres which 

 are passing from one hemisphere of the cerebellum to the other. 

 Intermingled with these bundles is a considerable amount of grey 

 matter. The continuation upwards of the pyramids of the medulla 

 (py) is embedded between these transverse bundles and separated 

 by them from the reticular formation. The olivary nucleus is no 



P 



TT 



FIG. 231. SECTION ACROSS THE PONS AT ABOUT THE MIDDLE OF THE FOURTH 



VENTRICLE. f 



y, pyramid-bundles continued up from the medulla ; po, transverse fibres of the pons passing 

 from the middle cms of the cerebellum, before (po ) and behind (po') the chief pyramid 

 bundles ; t, deeper fibres of the same set, constituting the trapezium ; the grey matter 

 between the transverse fibres is not represented either in this or in the two following 

 figures ; r, raphe ; o.s. superior olivary nucleus ; a. V. bundles of the ascending root of 

 the fifth nerve, enclosed by a prolongation of the grey substance of Rolando ; VI. the sixth 

 nerve ; n. VI. its nucleus ; VII. the facial nerve ; Vila, intermediate portion of the same 

 nerve ; n.VII. its nucleus ; VIII. anterior (superior) root of the auditory nerve ; n.VIll. 

 part of its outer or anterior (superior) nucleus ; v, section of a vein. 



longer seen, but there are one or two small collections of grey matter 

 which lie in the antero-lateral part of the reticular formation and are 

 known as the superior olivary nucleus (o.s.) The nerves which take 

 origin from the grey matter of this region are part of the eighth, the 

 seventh, the sixth, and somewhat higher up the fifth cranial nerves 

 (see figs. 231, 232). Of these the eighth and fifth take origin from groups 

 of nerve-cells which occupy the grey matter opposite the external border 

 of the floor of the ventricle ; the sixth from a group which is placed also 



