6o BULLETIN OF THE LABORATORIES 



this figure is drawn is a little smaller than the previous figures of the 

 medulla in order to represent the full section and show the relation of 

 the cerebellum to the medulla at this point. 



The entrance of the fifth nerve, a, is shown in quite a number of 

 sections of the series as the diameter of the root is so great, but we 

 here consider only two of this number. The one under present con- 

 sideration shows the fibres of the fifth nerve passing to a large motor 

 nucleus, 3, and to a sensory nucleus, r, also fibres passing to the gray 

 mass on the floor of the ventricle. The motor nucleus is charged with 

 very large multipolar cells with numerous processes and large nuclei. 

 For form and size, compare scale on Plate XVIII, Fig. 4. 



Passing to the next section (Plate XVIII, Fig. i,) taken at the 

 middle of the fifth root, we find about the same distribution of fibres 

 and nuclei. In no case are fibres of the fifth nerve traceable to the 

 cerebellum directly. The beginning of the large nucleus of the pons, 

 d^ also appears in this section. 



P'ig. 6, Plate XVIII, ])resents a longitudinal vertical section of the 

 medulla and cerebellum, showing the entrance of the fifth nerve, a, 

 and the eighth nerve, f, with its root nucleus, d. In the longitudinal 

 basal section of the medulla at the level of the eighth nerve (Plate 

 XVI, Fig. 6, ) the entrance of the fifth nerve, <:, is also seen with a 

 large bundle of fibres extending caudad and some turning to a nucleus 

 (probably motor) at d. 



At the entrance of the fourth nerve, in the section taken on a 

 level with the valve of Vieussens, the fibres of the fourth enter and 

 decussate with those of the opposite side, and then pass ventrad and 

 cephalad to their nucleus. The nucleus of the pons, a, is very large 

 and almost entirely surrounds the pyramidal tract, ,i,''. The cells of this 

 nucleus measure about .02-. 03 mm. and are imbedded in a dense neu- 

 roglia, their j)rocesses are short and the cells under a low power have 

 a (juite regular outline and bear a striking resemblance to the cells 

 clustered in the central gray mass bordering the aqueduct of Sylvius, 

 as will be seen by comparing Figs. 4 and 5, of Plate XVIII, taken 

 from the two regions. There appears to be another aggregate of 

 cells in the central gray mass at r, the cells of which are quite small, 

 flask-shaped, and bipolar, mostly measuring about .01 mm. The raphe 

 and the formatio reticularis are here highly charged with cells and pre- 

 sent the appearance of one large nucleus. 



Horizontal sections, including the anterior portion of the medulla 



