234 



THE ESSENTIALS OF HISTOLOGY. 



man, which lie in the ventral 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. 263, 264). 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 in the grey matter of the floor of the ventricle but nearer 



FIG. 263. SECTION ACROSS THE PONS AT ABOUT THE MIDDLE OF THE FOURTH 

 VENTRICLE. (Schwalbe.) f. 



Pl/> 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. 7., bundles of the ascending root of 

 the fifth nerve, inclosed by a prolongation of the grey substance of Rolando ; VI., root- 

 bundle of the sixth nerve ; n. VI., its nucleus ; VII., root-bundle of the facial nerve ; VII.u., 

 longitudinal portion of the same ; n. VII., its nucleus ; VIII. , (superior) root of the audi- 

 tory nerve ; n. VIII. , its nucleus ; v, section of a vein. 



the middle line, and the seventh partly from a special nucleus which 

 lies in the formatio reticularis, and partly from the nucleus of the sixth. 

 The fibres of the nerve first pass backwards to the floor of the ventricle, 

 then longitudinally upwards for a short distance, and finally bend 

 forwards and downwards to emerge between the transverse fibres at 

 the side of the pons. 



At the upper part of the pons (fig. 265) the fourth ventricle narrows 



