MOTOR NUCLEI IN PHYLOGENY 239 
From their nucleus of origin in the rostral end of the posterior 
visceral motor column the motor IX rootlets pass almost directly 
laterad and reach the periphery for the most part dorsal to 
the radix descendens trigemini (fig. 4). 
The dorsal motor vagus nucleus forms a somewhat slim cell 
column which tapers towards its caudal end. In the latter situa- 
tion the nuclei of either side lie dorso-lateral to the central canal 
and dorsal to the nucleus intermedius, being separated from one 
another by but a slight interval (fig. 1). Above the calamus 
these nuclei diverge from one another and lie within the gray 
matter of the ventricular floor as indicated in figure 3. 
The most caudal motor X rootlets pass out almost directly 
dorsal, intermediate members of the series course dorso-lateral 
to reach the periphery, while the rootlets arising towards the 
rostral end of the nucleus emerge as do those of the motor IX 
nerve. 
In Cacatua roseicapilla I have been unable to observe the 
origin of any undoubtedly motor vagus fibers from the cell column 
of the nucleus intermedius. In other words, no true nucleus 
intermedius X has been identified in this bird, though in the 
closely related form, C. galatea, Brandis (13) has described the 
origin of a few motor fibers from this source. In connection with 
this observation, however, the latter author noted that in parrots 
this cell group (which he termed the common X~—XII nucleus) 
was almost wholly concerned in the supply of the hypoglossal 
nerve. 
A small but evident ventro-lateral motor X nucleus is present 
in Cacatua. As in other birds this nucleus is not sharply cir- 
cumscribed, and its loosely arranged groups of multipolar cells 
occupy a position lateral and somewhat ventral to the large 
nucleus intermedius XII. Kappers (l.c.) has already drawn 
attention to the presence of this nucleus in other avian forms 
(Chrysomitris, Casuaris, Spheniscus, Colymbus), in which he 
has definitely established its motor vagus character. Brandis 
also had earlier described this nucleus (12, pp. 182-3) and had 
figured it in the guinea-fowl (l.c., Taf. XIII, Fig. 5, Numida), 
but he failed to recognize its significance as a source for motor 
