MOTOR NUCLEI IN PHYLOGENY 255 
It would appear from an examination of figure 12 that birds 
differ from the reptiles chiefly in the possession by the former of 
an acessory cell group of the oculomotor nucleus. This, how- 
ever, is not entirely true, for Kappers (34, pp. 63-64) has found 
in one specimen of Varanus sp.? a cell group which in the mor- 
phology of its elements and in its general relations resembles 
closely the avian accessory oculomotor nucleus. No oculomotor 
fibers could be distinguished arising from this unique accessory 
cell group in Varanus sp.? and no similar cell group was ob- 
served in any other Varanus specimens nor in any other reptile 
examined. 
Oculomotor nuclear differentiation in birds presents a marked 
advance over the condition obtaining in reptiles, especially in 
the differentiation of the median oculomotor cell group, since in 
none of the latter forms is a fully developed pars dorsalis of the 
median nucleus present. 
From the data at hand it would seem that among birds all 
three divisions of the oculomotor nucleus are well differentiated 
and that contiguity of the trochlear nucleus with the dorso- 
lateral oculomotor cell group is a constant character. On the 
other hand, there would seem to be a considerable amount of 
variation characterizing the relations of the associated oculo- 
motor and trochlear nuclei to the exit levels of the III and motor 
V roots, respectively. 
Fig. 12 Reconstruction charts of the oculomotor and trochlear nuclei in 
sauropsidan forms. A, Alligator sclerops (after Kappers, 34, fig. 60); B, Varanus 
salvator (after Kappers, 34, fig. 61); C, Spheniscus demersus (after Kappers, 9, 
fig. 77); D, Colymbus septentrionalis (after Kappers, 34, fig. 78); E, Ciconia alba; 
F, Cacatua roseicapilla. The reconstructions A, B, C, and D have been redrawn 
as mirror images of Kappers’ original charts, so that in the present paper both 
in these and in the other reconstructions the rostral end of the chart is toward 
the left side of the page. For comparison the drawings in this figure have been 
arranged so that the rostral ends of the trochlear nuclei are in line one below the 
other. See diagram above for explanation of signs. It is to be noted that no 
line of demarcation between the dorsal and ventral portions of the medial oculo- 
motor nucleus is indicated on these reconstructions. The ventral part of the 
median nucleus in the charts lies below the lower border of the dorso-lateral 
column, while the dorsal portion is above this line (cf. fig. 9, p. 25). 
