THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 21 
ite cell boundaries (figs. 26, 27, 28). Posterior to the ventro- 
lateral lateralis ganglion, the geniculate is uniform in structure 
and passes dorsally and posteriorly toward the medulla accom- 
panied by the root of the ventro-lateral ganglion. The posterior 
end of the geniculate ganglion is closely attached to the audi- 
tory ganglion, and near its entrance into the medulla, is joined 
by the root of the dorso-lateral lateralis ganglion; so that all the 
roots of the VII ganglion come into contact with the medulla 
near the same point and quite close to the entrance of the root 
of the auditory. The ganglionic complex of the VII has in gen- 
eral an arrangement quite characteristic for the Ichthyopsida 
(Herrick, ’99, Landacre, ’10) with the exception that it is quite 
easy at this stage in the development of Lepidosteus to separate 
the placodal or special visceral component from the neural crest 
or general visceral portion of the geniculate. 
The relation of the placodal portion of the VII ganglion to 
the endoderm of the hyoid gill pocket is of the greatest importance 
in forming a clear conception of the mode of origin and detach- 
ment of the placode. The hyoid gill pocket as it approaches the 
ectoderm gives off at this stage two solid processes of cells neither 
of which come into contact with the epidermis (figs. 14 to 16), 
but from an early stage up to the 8.8 mm. stage both these proc- 
esses are in contact with the epidermis. As they withdraw from 
the epidermis there appears a rather dense mass of mesoderm 
between the two processes and in the area between the processes 
and the ectoderm (fig. 19). This mass of mesoderm later devel- 
ops into the hyomandibular cartilage and muscles associated 
with this cartilage and the ear capsule. The dorsal process lies 
farther forward, considerably anterior to the anterior end of the 
geniculate ganglion. At the anterior end of the geniculate it 
has the appearance shown in figs. 14, 15, 16. The primordium 
of the hyomandibular cartilage lies between the hyoid pocket and 
the epidermis in a recess formed by the dorsal and ventral pro- 
longations of the endoderm and extends forward from this point. 
Four sections posterior to fig. 14 the ventral prolongation becomes 
detached and seems to disappear later, at the same time the dor- 
sal prolongation becomes shorter and seems to detach a mass of 
