250 DAVIDSON BLACK 
accessory cell group. Further, it will be evident that the tro- 
chlear nucleus at a more caudal level occupies a position analogous 
to that of the more rostrally situated dorso-lateral oculomotor 
cell group (fig. 9, f, g, and h). The practical absence of cells 
comparable to the numerous reticular elements characterizing 
this region in many mammals is a notable feature, though a well- 
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Fig. 8 Cacatua roseicapilla. Transverse section through the brain stem at 
the level of the junction of the middle and caudal thirds of the trochlear nucleus. 
Same magnification as figure 1. Ag. c., aqueductus cerebri; Coll., colliculus 
(= lateral mesencephalic ganglion of Wallenberg, 56); L.l., secondary cochlear 
tract (Wallenberg, 58); Lob. op., optic lobe; Nu. IV., trochlear nucleus; R. IV., 
homolateral trochlear root; R. mes. V., mesencephalic trigeminus root (van 
Valkenburg, 52 and 54; Miinzer u. Weiner, 438, Taf. VII); Tr. b.t., tractus bulbo- 
tectalis; Vent. op., optocoele. 
9 There can be no doubt that, both in Cacatua and Ciconia, oculomotor fibers 
take their origin from the cells of this nucleus. The origin of such fibers from 
this nucleus in birds was first noted by Brandis (16), who termed the cell group 
in question the Edinger-Westphal nucleus. Subsequently these observations 
have been independently confirmed by Cajal and Kappers and more recently 
by Brouwer (17). Kappers’ term accessory nucleus has been retained for con- 
venience in the present description. 
