442 
having here anastomosed with the main infraorbital canal, turns sharply 
backward and runs almost directly backward through the accessory 
nasal, nasal, and frontal bones, anastomosing again, by a terminal tube 
and pore, with the main infraorbital canal at tube No. 10 of that line. 
There was no connection whatever between the anterior end of 
that part of the canal that is enclosed in the nasal bone, and the hind 
end of the section of canal that is enclosed in the os terminale, such as 
COLLINGE describes, my work agreeing in this with Traquair’. 
The first sense organ of the supraorbital line lies, as stated above, 
in the os terminale. The second organ of the line lies in the accessory 
nasal bone, the third organ in the nasal bone, and the fourth, fifth 
and sixth organs in the frontal. The first and second tubes of the 
line lie, as stated above, at either end of the os terminale. The third 
tube of the line enters the canal as it passes from the accessory nasal 
to the nasal bone, its corresponding pore lying slightly postero-mesial 
to the nasal tube. The fourth tube enters the canal near the hind 
edge of the nasal bone, its pore lying somewhat mesial, or postero- 
mesial, to the posterior nasal aperture. The fifth and sixth tubes 
leave the canal as it traverses the frontal, the former lying about 
midway between the fourth and fifth organs of the line, and the latter 
about midway between the fifth and sixth organs. The seventh tube 
is the terminal tube of the line and has fused with the tenth tube of 
the main infraorbital line to form a double system that lies between 
the adjoining edges of the frontal, postfrontal, and squamoso-parietal 
bones, as already described. 
If the three sections of canal that, in Polypterus, lie in the os 
terminale, accessory nasal, and nasal bones, be compared with that 
part of the supraorbital canal that lies in the nasal bone alone of 
Amia, a striking similarity in the canals of the two fishes is evident. 
There are three sense organs in this part of the canal of each fish; 
the first pore, or group of pores, lies immediately posterior to the 
nasal tube; the fourth pore, or group of pores, lies mesial to the 
posterior nasal aperture; and the canal, in each fish, bends sharply 
backward at the point where tube No. 2 leaves it, this bend being 
much more pronounced in Polypterus that in Amia. Group 2 supra- 
orbital, in Amia, approaches but does not fuse with group 2 infra- 
orbital. In Polypterus the corresponding pores fuse. The agreement 
is so exact that it clearly establishes the homology of the three bones 
in the one fish with the single bone in the other. BripGE (No. 7), 
in one of the two specimens of Polypterus examined by him, found 
