ORIGIN OF JAW APPARATUS 381 
problems concerning the phylogeny of the organs of the verte- 
brate body. 
The solution here offered of the Trigeminal complex of Bdello- 
stoma is the outline of a new description of these nerves based 
on my investigation of the head nerves of this fish. Out of 
the several hundred dissections made in detail, to cover the 
relations of each nerve as completely as possible, finally came the 
realization that the trigeminal complex of Bdellostomais arranged 
after the Amphioxine plan and apparently inherited directly 
from Amphioxine ancestors. Although the relations of the 
five segmental nerves which compose the nerve supply of the 
Bdellostoma jaw apparatus are masked by being crowded together 
and bound up in dense connective sheaths, they can be made 
visible, and their homology then becomes evident. The figures 
31 td 35 are drawn from dissections and are selected from a large 
number made to illustrate the anatomy of these nerves. They 
show some details of root origins and terminal distribution of 
importance in establishing the structural similarity of the in- 
nervation of the jaw apparatus in Amphioxus and Bdellostoma. 
It is not intended to fully describe these nerves, but merely to 
present certain features pertinent to their comparative anatomy 
as Jaw nerves. 
A detailed account of the head nerves of Bdellostoma will be 
given in another contribution. Miss Worthington, Allis, and 
Miiller have described the head nerves in Bdellostoma and 
Fiirbringer and Bridge those of Myxine, to mention the more 
important contributions. The ophthalmic nerve is uniformly 
called the first or anterior nerve of the group. 
In order to lay bare the medullary bundles as they issue to 
make up the nerves, they must be freed from the connective 
tissue so abundant about and between the roots where they 
pass through the walls of the cranium and the ganglionic chamber. 
In Bdellostoma five nerves supply the jaw apparatus. They 
all leave the medulla cephalad of the ear capsule and, as the 
snout region extends far in front of the brain, the course of most 
of these nerves approaches the horizontal. From before, back- 
ward, they are: 
