The Cranial Nerve Components of Petromyzon. 157 
from the VII® ganglion. It is possible to suppose that the large 
dorsal branch contains the fibers derived from the trigeminus gan- 
glion. In this case the two branches would ceorrespond to the typical 
rami ophthalmiei superfieiales VII and V of selachians. 
The Acustico-facialis Complex. 
The arrangement of these roots and ganglia is exceedingly 
complicated and the task of giving a clear description of them is 
correspondingly diffieult. Differenees which seem to exist between 
this species and Lampetra have made the work of disentangling the 
several components more diffieult. As in Zampetra, there is a most 
dorsal root entering the lobus lineae lateralis and just beneath it a 
root entering the acusticum, both very compact and deeply staining. 
They are the neuromast roots. Beneath them is the large acusticus 
root, less compact. Beneath this and partly mingled with it is the 
small faseieulus communis root of very fine fibers. Still more ventral 
is the lateral motor root of VII. These are as in Zampetra. There 
must now be added a large component from the spinal V** traet, 
which is most ventral of all. This was not seen in Zampetra and 
the differences in the ganglia of the two forms supports the conelu- 
sion that if present there it must be much smaller than in the present 
species. There are thus six roots and five separate components to 
be traced and their distribution accounted for. The last four roots 
named are all very closely erowded together and to a considerable 
extent intermingled. Compare Figs. 4 and 5. 
The ganglionie complex is in three parts which must first be 
described separately: one within the auditory capsule, one beneath 
the middle of the capsule and one partly beneath the cephalie border 
of the capsule. That part of the ganglion within the capsule which 
belongs to the acusticus is not shown in the plate. Sections through 
the caudal part of the ganglion (379) show a very large number of 
quite small cells with apparently round nuclei (Fig. 5). These are 
the cells of the acustie ganglion which are disposed for the most part 
longitudinally and so do not show the spindle shape of cell bodies 
or nuclei in eross seetions. The ganglion spreads out laterally on 
the floor of the auditory capsule and a little fartber forward (370) 
a nerve goes from the lateral border of the ganglion under the 
auditory epithelium. From this point to the extreme cephalic end 
of the ganglion aeustieus fibers continue to go to the auditory epi- 
thelium. In this section 370 all the lateral part of the ganglion is 
