967 
giraffe, the two nuclei are connected right and left by a commissural 
nucleus in a very small region. Sometimes it also grows out laterally 
and projects over the pointed end of the central canai (fig. 2). Directly 
spinal from the calamus the nucleus has plainly shrunk in size; 
it becomes louse in: form and its medial pole turns upwards. 
After this we see a peculiar opening of the canalis centralis. 
This has already widened to a groove 2.2 mm. in length and 
in the middle 9.5 mm. broad. Soon the groove deepens pit-like 
towards the back, and when it breaks through at the back wall of the 
oblongata it is 1.5 mm. deep and 0.830 mm. wide. The pointed 
ends of the central canal ean still be found in many sections as 
tapering bulgings of the base of the IV ventricle. The latter, by 
Fig 2. Phocaena communis. 
Nucleus motorius commissuralis vag). 
reason of the said conditions in the caudal portion, assume a shape 
unusual in mammals, as the irregular walls of the deepest part are 
perpendicular and the base stretches out right and left like a groove 
(fig. 3). Well developed epithelium is neither present here, and the 
place of opening is therefore entirely filled with cell-remnants. The 
dorsal motor vagus nucleus has now grown thicker and has quite 
turned upwards again; it is strongest in the middle, has crept up 
against the above-mentioned perpendicular portion of the ventricle 
wall and soon spreads out with scattered cells in a curve laterally 
under the ependyma. In a few sections a distinet continuation is 
to be seen in a ventro-lateral direction, on the significance of which 
1 shall venture shortly to express an opinion (fig. 3). In this region 
the nucleus contains two types of cells differing in size; it is often 
loosely built and very different in size, with a maximum of 40 cells. 
These conditions hold for many sections further frontally. Mean- 
while the groove-like continuations of the base of the IV ventricle have 
grown smaller; soon they disappear, the perpendicular walls keeping 
their place for some time. The nucleus, especially in the medial 
portion, has become thicker; it shows at this place a club-like 
