975 
d. very lateral, near the latero-caudal border of the posterior horn. 
The opinion that these last cell-groups lying latero-dorsally belong 
to nucleus XI [ base upon the following considerations : 
1. The cells are of the same type. 
2. They occur periodically, like the medial nucleus group at the 
well-known place. 
3. They send out distinct continuations near the calamus, in the 
direction of the medial group. 
4. The efferent XI roots follow the shiftings of these latero-dorsal 
groups, which shiftings have to do with the position of the posterior 
horn, which is pointed the most upwards spinally. 
The XI nucleus in Phocaena in general bas relatively small cells 
and is poorly developed at most places. 
The oliva inferior of the porpoise commences immediately behind 
the calamus and continues frontally as far as into the region of the 
nucleus facialis. It is particularly well developed, commences with small 
cells at the base of the raphé, and immediately grows out parallel to 
the front wall of the oblongata. Very soon it becomes thicker, the 
cell type becomes larger, and cells of the same type appear in the 
raphe (I of fig. 10).Rather more frontally a second, quite independent, 
group appears, just below the surface, much smaller and quite lateral 
from the former group. The medial portion grows rapidly and 
stretches laterally in a point, thus following the frontal wall of the 
oblongata; the middle olive likewise becomes thicker, and the 
lateral portion remains relatively small. Very speedily a third small 
group appears laterally (II of fig. 10). The large medial portion is 
at first separated from the frontal wall by are-fibres which issue from 
the raphe. This fibre system grows much stronger, and in it we see 
a new group appear, again independent of other groups. 
The middle olive above-mentioned has disappeared, now however, 
in the ventral portion of the raphé, cells appear which rapidly 
increase in number right and left in the heavy arc-fibre system 
ventrally from the medial olive, This increase is so rapid that a 
dorsal and a ventral medial olive can soon be distinguished (II of 
fig. 10). The raphe cells have then disappeared. Now the lateral 
portions of the large complex diminish, the dorso-medial olive likewise 
grows poorer, while the ventro-medial portion, on the contrary, 
grows heavier and heavier. It bends dorsally in a strongly lateral 
curve, ventrally it follows, also in a curve, the frontal wall of the 
oblongata, so that the whole has the appearance at this place of a 
gigantic comma. The dorso-medial portion has then greatly decreased. 
63 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
