ALLIS. VoL. XII. 
51 
cranial cavity, a comparatively long distance from its point of 
origin on the under surface of the brain, to the front edge of 
the horizontal process of the petrosal. There, immediately 
behind and internal to the place of exit of the main facial 
nerve, it pierces the membranous roof of the eye-muscle canal, 
and lying in a semi-circular foramen (adfr, Fig. 11, Pl. XX1), 
at the angle formed by the horizontal process of the petrosal 
and the process of that bone that forms the front wall of the 
utricular fossa, enters the eye-muscle canal. Turning down- 
ward it separates into two main parts which, separating again 
into two or more parts, enter the externus while that muscle is 
still inside the canal. 
The rectus externus is sometimes double through part of its 
length, one part lying, relatively to the eye, directly external to 
the other. 
Schneider (No. 112, p. 10), after describing the origin and 
intracranial course of the abducens in Acipenser, says that 
that nerve in all ganoids enters the orbit, as it does in Aci- 
penser, at the front under corner of the Gasserian ganglion, 
and that, in its further course, it lies in all, Amia included, 
under the ophthalmicus trigemini, but over all the other 
branches that arise from the trigeminal ganglion and have 
a forward course. Just what is meant by “over all the 
other branches”’ is not entirely evident from this statement 
taken alone, but in his Fig. 5@ he shows the arrangement 
of all the nerves concerned in Lepidosteus. In that figure 
the abducens, after leaving the inner, anterior surface of the 
Gasserian ganglion, crosses, from within outward, under the 
r. ophthalmicus superficialis trigemini and over, that is 
across the upper surface of, the truncus maxillaris trigemini 
and r. buccalis facialis. It cannot, therefore, be doubted that 
this is the further course ascribed to the abducens in all 
ganoids. This, it will be seen, is markedly at variance with 
what is found in embryos and in the adult of Amia, and I can 
in no way account either for his observation or his statement. 
As I differ as markedly and unaccountably from him in certain 
other of his statements, I have not been able to accept any of 
his results without much reservation. 
