272 DAVIDSON BLACK 
reduction in the number of elements originally present and not to 
the retention of a primitive character. 
In the great development of the hypoglossal component of 
their intermedius motor complex, it has been shown that parrots 
differ from all other birds. This fact would appear to be corre- 
lated with the exceptional development and differentiation of the 
intrinsic tongue musculature among members of the parrot 
family. In its morphology and relations the hypoglossal nu- 
cleus in parrots resembles in many respects that of mammals, 
though the peculiar psittacine nucleus cannot well have been 
evolved as other than a specialization of what has already been 
termed a typical avian intermedius complex (vide supra)... 
Intrinsic oculomotor nuclear differentiation has attained to a 
high state of complexity among birds, and the ground-plan of 
this avian oculomotor specialization is essentially similar to 
that obtaining in this nucleus in many mammals. In this con- 
nection it is significant that Kappers has described an arrange- 
ment of the intrinsic oculomotor nuclei in one specimen of Vara- 
nus sp.? which closely resembles that obtaining in birds (vide 
supra, pp. 255 and 270). The occurrence of this phenomenon in a 
modern reptile shows definitely that the ground-plan of the nu- 
clear differentiation characteristic of this region in higher forms 
has already been determined within the class from whose pro- 
totypes both avian and mammalian forms were evolved. 
Finally, it would appear that modern birds and reptiles while 
presenting minor resemblances, show a fundamentally different 
plan of organization in the arrangement of their cerebral motor 
nuclei, though either avian or reptilian motor pattern could well 
have been evolved from a form whose nuclear organization was 
of a type similar to that obtaining in some modern anurans 
(e.g., Rana catesbiana, fig. 14 B)!”7 or urodeles (e.g., Triton, 
fig. 14 A). 
17 It has previously been pointed out (9, p. 423) that though the anuran type 
has certainly been evolved comparatively recently in vertebrate phylogeny, 
yet ‘“‘within the brain stem in Rana a motor nuclear pattern obtains which on 
first examination would seem to be much more primitive than the motor nuclear , 
pattern in selachians.” : 
