The Cranial Nerve Components of Petromyzon. 179 
arises from the larger part of the same motor nueleus. The dorsal 
strand becomes indistinguishably incorporated into the motor trige- 
minus before it passes through its foramen (Fig. 3). The strand is 
smaller, both actually and relatively, than the corresponding root in 
Lampetra and is sooner lost in the trigeminus root. ÖOutside the 
cranium, however, there soon appears in the most mesial part of 
the trigeminus ganglion a small bundle of fibers which soon becomes 
rounded and very distinet. This runs forward to the front end of 
the trigeminus ganglion, erosses laterad in the angle between the 
trigeminus and profundus, close upon the cephalie face of the maxil- 
laris trunk at its base, and enters the muscle on the caudal surface 
of the eyeball, the recetus posterior. In these sections there is noth- 
ing to show that the nerve which innervates this musele is com- 
posed of the fibers of the smaller motor root, or that it is not. The 
same is true in ZLampetra, but in P. marinus, fluvvatilis and planeri 
the small root is said to be traced directly to the muscle. 
Here we have a clear contradietion between our supposed facts 
and the theory that museles derived from the somites are innervated 
by ventral motor nerves, and museles derived from lateral mesoderm 
by lateral motor nerves. The issue is so clear and the matter of 
such importance that a further investigation of the subjeet will be 
awaited with the greatest interest. In this investigation two possi- 
bilities should be held in mind: the muscle may prove to be derived 
from the lateral mesoderm; or, the nerve which supplies it may be 
composed of those fibers in the trigeminus root which arise from 
the ventral motor column at the level of the facialis. These fibers 
are present in both P. marinus and Lampetra and if they do not 
innervate this muscle, their very presence in the trigeminus consti- 
tutes an additional problem; namely, what somatie muscle do they 
innervate by way of the trigeminus? To deeide these points it 
will be necessary to have GoLGI preparations in which these parti- 
cular fibers are well stained through their whole central and peri- 
pheral course. 
The Spinal Nerves. 
Spinal dorsal 1 arises at 459, inclines forward and passes 
through the eranium at 455, has a small ganglion” mesial to that of 
the N. lineae lateralis, erosses laterad between the lateral line gan- 
glion and the cardinal vein, erosses the eephalie surface of the dorsal 
ramus of sp.ven. 2, enters a muscle septum dorso-laterally and is 
