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, b, and to a sensory nucleus, c, 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, 
dj also appears in this section. 
Fig. 6, Plate XVIII, presents a longitudinal vertical section of the 
medulla and cerebellum, showing the entrance of the fifth nerve, a, 
and the eighth nerve, c, 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, g. The cells of this 
nucleus measure about .02-. 03 mm. and are imbedded in a dense neu- 
roglia, their processes are short and the cells under a low power have 
a quite 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 c, 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 
