514 ALLIS. [VoL. XII. 
into the orbit. The opening, however, is much larger than is 
necessary simply for the passage of the vessel, and it therefore 
forms a true fenestration of the side wall of the orbit, compara- 
ble in every respect to the larger and more important one 
described by Sagemehl in other fishes. Sagemehl gives no 
name to the opening, referring to it in the text as the fenestra- 
tion ff, letters which do not appear in the figures. I have called 
it the orbito-nasal opening or fenestra. That part of the olfac- 
tory canal that lies in front of it is formed by the fusion of 
two canals, the olfactory canal proper and another canal, quite 
probably the homologue of the orbito-nasal canal of selachians 
(No. 44, p. 73). That canal in selachians is traversed by what 
from Gegenbaur’s description is apparently, and in Callorhyncus 
(No. 116, Fig. 1, and No. 59, p. 265) and Mustelus (No. 123, 
Fig. 1), judging from the figures alone, by what is certainly the 
ramus ophthalmicus profundus; but neither Gegenbaur, Stan- 
nius, Hubrecht, nor Tiesing mentions or shows the passage of a 
vein with the nerve. In Torpedo and Raja, Tiesing (No. 123, 
Figs. 2 and 3) shows the profundus passing with the super- 
ficialis through what Gegenbaur calls in the former the pre- 
orbital incisur and in the latter the preorbital canal. What 
passes through the orbito-nasal canal, the orbital opening of 
which is shown by Tiesing in Torpedo but not in Raja, is not 
indicated. In Amia there is no ophthalmicus profundus, but 
in Polypterus that nerve is found and it passes (No. 93, p. 394) 
from the orbit to the cartilaginous nasal capsule through a 
“canal in the ectethmoid bone, which it occupies together with 
the ophthalmicus superficialis, the obliquus superior muscle and 
a considerable vein.” That there must be some canal or 
channel in elasmobranchs for the passage of this vein so large 
and important in Amia, and that it is probably the orbito-nasal 
canal, seems sufficiently evident to warrant the use I have made 
of the name. 
The development of the olfactory nerves and their canals in 
Amia is as follows. In specimens less than 10 mm. in length 
the preorbital processes have not yet been fully formed, and the 
orbit on each side is directly continuous with the olfactory pit ; 
the two regions being separated by an elevation, the beginning 
