CRANIAL NERVES OF SIREN LACERTINA 291 
portion of the auditory ganglion lies within the skull (figs. 32-36). 
The cells of the posterior part are small and of one size; the cells 
of the anterior part are of two kinds, one kind appearing identical 
with those of the posterior part and situated ventrally, the other 
larger-celled portion being dorsal. These two kinds of cells in 
the anterior part of the ganglion evidently correspond to the med- 
ium and large sized fibers which innervate the utriculus and the 
anterior and horizontal canals. The fibers of this anterior part of 
the ganglion seem to correspond to the anterior ventral rootlet of 
the auditory nerve. 
The ventral division of the lateral line fibers of the facial nerve, 
after giving off the small constituent which rejoins the dorsal 
division, as described above, descends to the dorsal border of the 
anterior portion of the auditory ganglion, and at the anterior end 
of the latter, as the anterior division of the auditory nerve enters 
the ear capsule, joins the motor and general cutaneous constitu- 
ents of the facial nerve and with the latter, entering the facial 
canal in the petrosal cartilage, forms the truncus hyomandibu- 
laris VII, and passes into the ventral lateral line ganglion (fig.13). 
Anteriorly the auditory ganglion becomes confluent with the 
ventral lateral line ganglion. The latter (gllv.) is an elongate, 
almost cylindrical mass of cells on the truncus hyomandibularis, 
and is confined to the peculiar canal in the petrosal through which 
the truncus emerges from the skull. 
The geniculate ganglion (gen.) extends anteriorly from the medial 
anterior end of the ventral lateral line ganglion in an extension 
of the facial canal which re-enters the cranial cavity where the 
geniculate ganglion becomes confluent with the Gasserian ganglion, 
as already described, although usually the two ganglia are easily 
differentiated from each other (fig. 36). 
These six ganglia, dorsal lateral line, Gasserian, geniculate, 
general cutaneous VII, ventral lateral line and auditory, make 
a continuous ganglionic mass in which often there is difficulty 
in distinguishing the individual ganglia. The geniculate ganglion 
in Siren is much more distinct than in other Urodela hitherto 
described. 
