No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 599 
this part of their course, in the thin membranous covering of 
the nasal sack. There is no ethmoid canal in Amia, and as that 
canal is found in Polypterus (No. 93) it would seem to depend 
on the presence of a ramus ophthalmicus profundus, and on the 
partial fusion of the canal for that nerve with the canalis pre- 
orbitalis. If, then, the canal for the profundus in Polypterus is, 
in its proximal portion, the orbito-nasal canal of selachians, as 
seems probable, that canal must sometimes in ganoids fuse with 
the preorbital canal, as in Polypterus, and sometimes with the 
olfactory canal, as in Amia. In selachians the distal portion 
of the canal seems to fuse with or become the ethmoid canal, 
for Gegenbaur, in all his ventral and lateral views, never gives 
but one anterior opening, calling it sometimes the distal open- 
ing of the ethmoid canal and sometimes that of the orbito-nasal. 
There may even be two canals for the profundus in selachians : 
one, the ethmoid canal, for the dorsal branch of the nerve, 
Ewart’s nerve on! (No. 29, Fig. 2) ; and one, the orbito-nasal, 
for its orbital branch, Ewart’s nerve ov. Ewart unfortunately 
does not describe the course of the latter. It would seem, 
however, from its name to remain in the orbit. 
Immediately after issuing from its foramen, the ophthalmi- 
cus trigemini gives off two branches one of which arises from 
the outer and the other from the inner surface of the nerve. 
These branches are flat and broad at their bases, and closely 
embrace the ophthalmicus facialis. They run upward and 
backward, one on either side of the facialis, pierce the alisphe- 
noid, and, entering the cartilage of the cranium by the same or 
by closely adjoining canals, issue on its upper surface either by 
the same or by adjoining foramen. They are the first two, or 
first pair, of frontal branches of the nerve, and the course and 
position of the canal or canals traversed by them, as also that 
of the other small canals traversed by other frontal branches 
of the nerve, vary greatly in different specimens. There are 
frequently both in the young and in the adult, small branch 
canals connecting these canals and giving passage to delicate 
anastomosing branches of the nerve. 
One of these first two branches of the ophthalmicus tri- 
gemini is accompanied by the first branch of the ophthalmicus 
