CRANIAL NERVES OF SILURUS AND MORMYRUS 33 
The motor X roots are very small (fig. 19). They originate 
from a continuous column, of which the frontal extremity (which 
probably contains also motor VII and IX cells) is shifted in a 
ventro-lateral direction, as is often found in teleosts, as in the 
Pleuronectidae and in Gadus (in the latter this part even forms a 
separate group).’7 The ventro-lateral migration of this part has 
apparently taken place at the expense of the cells which were 
originally dorsal and which have disappeared in that region or 
become very few. 
The cells of this column (fig. 19) are not very large as contrasted 
with the reticular cells which are scattered along and below the 
fasciculus longitudinalis posterior. 
The motor roots—both those from the ventral and from the 
larger dorsal part—leave the bulb together with the sensory 
roots. Proceeding caudally the dorsal nucleus becomes stronger 
and consists of cells which resemble very much those of the tro- 
chlear nucleus and have a fan-like arrangement. 
On the left side of my sections (the one that is represented in 
my diagrams) the spino-occipital roots could not be traced on 
account of injuries to the ventral part of the bulb on that side. 
The right side, however, showed the first spino-occipital root 
as a fairly strong root. The frontal limit of the spino-occipital 
column can, however, not be stated with exactness on account of 
the presence of a great many reticular cells in that region of the 
bulb. This is the reason why the spino-occipital column has not 
been indicated in my diagram. 
The vestibulo-lateralis apparatus in Mormyrus shows great 
deviation from the normal condition in teleosts, this being chiefly 
caused by the hypertrophy of the primary, secondary and tertiary 
centers of the lateralis nerves, the peculiar development of which 
has several times given rise to misinterpretations of the brain 
of the Mormyridae, as recently by Franz (loc. cit.). 
Aside from this author there have been others who made a 
similar mistake. Thus Sanders has ascribed the peculiar develop- 
37 Kappers, Die phylogenetische Entwicklung der motorischen Wurzelkerne 
in Oblongata und Mittelhirn. Folia Neurobiologica, Bd. 6, Sommer-Ergiinzungs- 
heft, p. 29. 
