977 
have grown smaller and disappear by degrees. In the following 
stage the dorso-medial portion of the olive is entirely gone, the 
ventro-medial, on the contrary, is particularly powerfully developed 
and much turned upwards (VL of fig. 10). The portion through 
which the XII roots now make their way shrinks and also disappears. 
Soon after, however, while the ventro-medial portion is becoming 
heavier, we see a new group appear, also medially from the efferent 
hypoglossus root (VII of fig. 10). This group also develops rapidly, 
first in a ventro-lateral direction, after which it takes a hook-like 
bend near the frontal wall of the oblongata. The original lamella of 
this group grows up so high that its top reaches the level of the 
main mass lying medially. The latter is now particularly well 
developed, except that at the base it is not so broad as before 
(VII of fig. 10). The medial lamella of the last group also grows 
upwards though not to such an extent as the lateral one. After this 
the whole complex diminishes. The medial main mass remains the 
largest and longest, till finally this also shrinks rapidly and disappears 
in a few sections. For reference I have given in Fig. 10 under 
each diagram the number of sections frontally from the calamus, 
with the indication of the place of which the diagram is made. 
In several mammals a strong development of the oliva inferior is 
accompanied by a slight development of the nucleus reticularis inferior. 
As might be expected therefore, this reticular nucleus in the porpoise 
proves to be very poor considering the great size of the olive inferior. 
Simultaneously with the olive, and ventrally from the radix de- 
scendent V, a group of cells appears which for reticular elements are 
small. With the appearance of the ventro-medial olive, small raphé 
cells make their appearance in the dorsal portion of the raphe, and 
we also see directly dorsal from the dorso-medial olive a small- 
cellular nucleus. Further frontally severat smaller groups of reticular 
cells occur very inconstantly in the substantia reticularis. Only the 
ventro-lateral portion extends in an upward direction towards the 
side wall of the oblongata, all the vest remains poorly developed 
and frequently inconstant. With the olive the elements of the reticu- 
laris group also disappear. 
The considerable development in Phocaena communis of the dorsal 
motor vagus nucleus and its extension with the commissural nucleus 
has to do with the size and the construction of the stomach in this 
animal. (Max WeBer, Studien über Säugetiere. Ein Beitrag zur Frage 
nach dem Ursprung der Cetaceen; idem Anatomisches über Cetaceen, 
63* 
