244. DAVIDSON BLACK 
VII motor nucleus is larger in Ciconia and occupies a more 
caudal position than in Cacatua (cf. fig. 16 C and D, p. 260). 
With the exception of Casuaris, in all the avian forms in which 
these relations have been carefully established (Colomba, Chry- 
somitris, Ciconia, Spheniscus, Colymbus, Cacatua) the motor 
VII nuclei are situated rostral to the exit level of the motor 
Vil root. This relation, as Kappers has repeatedly noted, serves 
to distinguish these forms from all other vertebrates. In Casu- 
aris, on the other hand, the motor nucleus lies on the level of its 
root exit in a relation somewhat similar to that obtaining in 
Rana catesbiana and Petromyzon (figs. 13,14, 15, and 16). 
Brandis (14) has recognized but one motor VII nucleus in 
each of the forms which he described, though Kappers’ (82) 
subsequent careful investigations have shown that, at least in 
the case of Columba, Brandis’ observations were in error. How- 
ever, this does not serve to discount wholly the latter author’s 
observations on the motor facial nucleus in other avian forms, 
since it is quite probable that not all birds possess two motor 
VII nuclei (e.g., Casuaris). 
Nerve VI 
The abducens nucleus in Cacatua forms a well-marked cell 
column of large multipolar cells which occupy a dorsal position 
in the formatio reticularis, to the lateral side of the fasciculus 
longitudinalis medialis (figs. 5 and 6). The nucleus lies almost 
wholly rostrad of the exit level of the motor VII root, and ex- 
tends from this level approximately to that of the caudal border 
of the motor V root (fig. 16 D, p. 260). The abducens roots are 
five in number and emerge in series on the periphery rostrad of 
the exit level of the motor VIT root. 
In Ciconia the abducens nucleus occupies a somewhat more 
caudal position than in Cacatua and is considerably longer in 
rostro-caudal extent, though its position within the formatio 
reticularis in the two forms is similar. Eleven small emergent 
abducens rootlets were identified in Ciconia, all of which emerge 
in series rostrad of the exit level of the motor VII root. 
