MOTOR NUCLEI IN PHYLOGENY 235 
ventral nucleus Brandis’ term ‘nucleus ventralis hypoglossi’ 
(13) has been retained.? 
In Cacatua the nucleus intermedius XII forms a well-marked 
column of large multipolar cells which rests throughout its ex- 
tent upon the periphery of the periependymal gray matter and 
is at all levels quite sharply demarcated from the adjacent nu- 
cleus motorius dorsalis X (figs. 1 and 3). In the closed portion 
of the medulla it lies ventro-lateral to the central canal, there 
being in this form a relatively large amount of periependymal 
gray matter between the latter structure and the dorsum of the 
raphé (cf. figs. 1 and 2). In this character Cacatua, in common 
with other members of the parrot family, differs from Ciconia 
and most other birds (Brandis, l.c., p. 631). In the open por- 
tion of the medulla the nucleus intermedius XII occupies an 
analogous position beneath the floor of the fourth ventricle. 
Except at its rostral extremity, the area of the nucleus inter- 
medius XII in cross-section is considerably greater than that 
of the dorsal motor vagus column, while in total length the 
former nucleus exceeds the latter and extends caudally for 
some distance beyond it (fig. 16, D, p. 260). Around the nucleus 
and within its interstices, numerous very fine oblique and longi- 
tudinally arranged medullated fibers are to be seen which give 
to it a very characteristic stippled appearance on section. These 
strands constitute the fibrae propriae nuclei hypoglossi of Koch 
(37), to which Brandis has also drawn attention (l.c.). 
The root fibers arising in the nucleus intermedius XII, which 
in Cacatua constitutes the chief source of the hypoglossal nerve, 
converge for the most part towards the ventro-medial margin 
of this cell group. Here they become combined to form well- 
marked nerve strands, which then pass obliquely ventral and - 
lateral to reach the periphery approximately along the lateral 
border of the inferior olivary nucleus. As in other birds, none 
® The term nucleus intermedius, pars hypoglossi (or simply nucleus inter- 
medius XII) is synonymous with Brandis’ (l.c.) hypoglossal portion of the common 
vago-hypoglossal nucleus. The nucleus ventralis XII is equivalent to the nucleus 
XII of Turner (50) and of Kappers (88, fig. 5) as well as to the latter author’s 
‘Fortsetzung des Cervicalmarks’ (9). 
