MOTOR NUCLEI IN PHYLOGENY 555 
these forms. Certain it is that the dorsal and ventral cell 
‘groups of the oculomotor nucleus are definitely placed in rela- 
tion respectively to the dorsal and ventral decussations of the 
tecto-bulbar tracts (66). 
The differentiation of the elements of the oculomotor nucleus 
into dorsal and ventral moieties reaches its maximum develop- 
ment in fish, among members of the teleostean group. The 
probable significance of the presence of dorsal and ventral oculo- 
motor cell groups among ganoids has already been alluded to 
and it remains only to point out that this differentiation, which 
apparently must have been already forecast if not completed 
in the ancestral teleostome stock, would seem to be correlated 
rather with specialization in intrinsic effectors than in the 
extrinsic oculomotor apparatus. The reason for such.a supposi- 
tion becomes evident when it is recalled that, among modern 
fishes, in the general arrangement of the extrinsic oculomotor 
apparatus there are no characters of a truly fundamental nature 
distinguishing teleostomes from selachians (Harman, 33; Herrick, 
34; Workman, 98). 
In the unusually small size of its trochlear nucteus Solea pre- 
sents a marked contrast to the condition obtaining among other 
members of the flat-fish group in which, as in Lophius, this 
nucleus is well developed. In this connection the observations 
of Harman (I. c.) are of further interest. This investigator has 
pointed out that among flat-fishes the superior oblique muscle 
is of unusually large size relative to the other eye muscles and 
that in general, in fish when the visual axes are capable of con- 
vergence, there occurs a specialization of the m. obliquus su- 
perior. In view of this, it is possible that further investigation 
may show that the small size of the trochlear nucleus in the speci- 
men of Solea here studied is merely an individual variation. 
CONCLUSION 
Among myxinoids the most important information concerning 
environment must reach the central nervous system through 
olfactory or tactile channels. The restrictions imposed upon 
these forms by the absence of a functional visual apparatus 
