BULLETIN OF THE LABORATORIES 
56 
XIV, Fig. 3.) The median nucleus {Fig. 5, < 5 ,) still continues, and 
there is a gradual separation of the cells of the nucleus into a dorsal 
and ventral group, as will be seen by reference to Fig. 6, d, and e, of 
the same plate. The remaining portions of the gray matter are about 
as in the previous section. At about the middle of the decussation 
we find that the median nucleus has entirely differentiated into two 
distinct nuclei, the ventral being themaudad extension of the nucleus 
of the twelfth nerve, (Plate XiVy;.?^/^. 4,) and the dorsal, the nucleus 
of the eleventh nerve. The •pyrafijiidal tracts in decussating and pass- 
ing dorsad are divided up into a great many fasciculi, and these are 
thickly interwoven with each other in crossing and also with the fibres 
of the gray matter. 
The surface of the fasciculi is very thickly covered with nutri- 
tive corpuscles, even more so than the gray matter at this point. The 
gray matter contains many longitudinal bundles which are seen here 
in cross section and which mark the first appearance of the formatio 
reticularis ,of the medulla. In this section also there appears for the 
first time a small ventral cluster of cells, (Plate XIV, Fig. 6, a,) which 
marks the beginning of the olivary body. These cells are rather smaller 
than those in any nucleus- previously discussed, measuring about. 02 
mm. in diameter. They tend to be bipolar and flask shaped in form 
and the processes start more abruptly from the cell body. Plate XIV, 
Fig. 2, represents this entire nucleus. 
It may be noted here that our study has led us to the opinion that 
most of the so-called flask -shaped and unipolar cells are in reality 
cells of the bipolar type which have been sectioned obliquely to their 
axis. This will account for the fact that many of the flask-shaped 
cells are non-nucleated. We do not mean to imply that there are no 
unipolar cells, for those do in some cases undoubtedly exist, but that 
in a nucleus the cells all tend to be of the same type and it is with 
doubt that we accredit the presence of unipolar cells in a multipolar 
nucleus. 
Passing cephalad from this level, the medulla, enlarges rapidly, 
the C'Tialis centralis is flexed dorsad and rapidly expands into the fourth 
ve Uricle. There is an aggregation of gray matter towards the median 
portions and on the floor of the ventricle. The white matter is limited 
to a narrow zone around the lateral and ventral surface and the reticu- 
lar formation. 
In a section taken at the level of the twelfth nerve, (Plate XV,^ 
