No. 3.] LATERAL LINE OF AMIA. 471 
1. /nfra-orbttal Canal.— The infra-orbital is the main canal of 
the system, and is directly continuous with the lateral canal of 
the body. It has four parts or regions, which develop some- 
what independently: an antorbital, a suborbital, a squamosal 
or temporal, and a post-temporal, —all continuous in the adult. 
The antorbital part of the canal begins at a sharp bend in the 
suborbital portion, immediately in front of the eye and below 
the posterior nasal aperture. It runs forward and downward, 
and partly encircles the nasal tube (which in Amia is the ante- 
rior nasal aperture), running below and in front of it, and unit- 
ing, on the top of the snout between the nasal tubes, with the 
corresponding canal of the opposite side of the head. This ant- 
orbital portion, which is more properly an anterior cross-com- 
missure connecting the two main infra-orbital lines, seems to be 
found in some other ganoids; for Traquair (No. 18, p. 181) 
describes a similar connection in Polypterus bichir, and Leydig 
(No. 9, p. 249) three of them in Chzmcera monstrosa,; but it is 
not found in the teleostei, so far as can be judged from the 
descriptions I have been able to find. According to Sagemehl 
(No. 14, p. 36), it does not exist in the Characinidz, nor is it 
found in Amzurus catus (No. 21, p. 265), and from my own exami- 
nations I know it is not found in Salvelinus namaycush, Microp- 
terus dolomieu, E:sox luctus, or Stizostedium vitreum. In Salve- 
linus, a line of organs lying wholly in the external epidermis, 
occupies about the position of the canal in Amia. These organs 
belong to the same class as the canal organs. There are several 
other lines on the head of Salvelinus, and corresponding ones 
on that of Amia. 
The suborbital part of the infra-orbital part is, in the adult, 
connected at its anterior end, immediately in front of the pos- 
terior nasal aperture, with the supra-orbital canal. There is no 
direct union of the two lines here, the connection being of the 
nature of a commissure formed by the anastomosis of two 
dendritic systems, one of which is the terminal system of the 
suborbital, and the other the fourth regular system of the supra- 
orbital canal. Starting from this point, the suborbital canal 
runs forward and downward to a point above the anterior end 
of the maxillary, where it is joined by the antorbital canal or 
anterior commissure; it then turns sharply backward, and lying 
above the upper edge of the maxillary and jugal and below the 
