437 
moidal organ and the second organ of the line, which lies in the 
premaxillary, is, accordingly, numerically the second tube of the line, 
and will be so considered. This tube and its associated pore are not, 
however, a simple tube and pore, but are what I designated in my 
work on Amia as double tubes and pores, being formed by the fusion 
of the second tube and pore of the main infraorbital line with the 
second tube and pore of the supraorbital line, as will be shown in 
describing the latter canal. 
Having entered the premaxillary bone the main infraorbital canal 
runs at first laterally, then backward and laterally, and then upward 
laterally and backward through the bone, passing, in its course, around 
the anterior and lateral edges of the base of the nasal tube. In this 
premaxillary section of the canal there are three sense organs, the 
second, third, and fourth ones of the line. Between the second and 
third organs a tube is sent almost directly forward, and opens by a 
single pore immediately anterior to the nasal tube. Between the third 
and fourth organs a tube is sent downward forward and laterally, at 
right angles to the canal, and opens by a single pore which lies lateral 
to and below the nasal tube. At the hind edge of the premaxillary, 
between it and the next following bone, the fifth tube of the line is 
given off, the associated single pore lying immediately antero - ventral 
to the posterior nasal aperture. This pore lies dorsal to the deep 
furrow that lies between the outer and inner folds of the upper lip of 
the fish, the two preceding pores lying ventral to the shallow anterior 
end of the furrow, and hence in the lip itself. 
On comparing that part of the infraorbital canal of Polypterus 
that lies in the ethmoid and premaxillary bones, with the anterior 
portions of the same canal in Amia, it is evident that the second and 
third organs of the line, in each fish, occupy very closely corresponding 
positions relative to the nasal tube, and as that tube is an important 
anatomical landmark it seems highly probable that the bones that 
enclose the two organs, in the two fishes, are homologous. But in 
Amia one of these organs lies in the lateral half of one half of the 
single ethmoid of the fish, and the other in the anterior portion of 
the antorbital; while in Polypterus they both lie in the premaxillary, 
My conclusion, in one of my earlier works (No. 4, p. 453), that the 
ascending process of the premaxillary of Teleosts and Urodeles is formed 
‚ by the fusion of the ethmoid of Amia with the premaxillary of that 
same fish thus seems confirmed, the whole of the ethmoid of Amia, 
however, not perhaps taking part in the fusion. The homologue of 
the remaining, median portion of the bone of Amia, may, perhaps, 
