482 ALLIS. [Vou I. 
operculo-mandibular canal which comes up through the pre-oper- 
culum. At the point of union a double system is formed by 
the fusion of system 17 infra-orbital with 17 operculo-mandibu- 
lar; but the trunk of this system has been pushed out of its 
proper place down into the opercular line, and les with all its 
branches in the dermal tissue between the upper end of the pre- 
operculum and the lateral edge of the squamosal. Its primary 
branches are not so widely separated as those of the double 
trunk 15-7. They are directed one forward and the other 
backward, with all their branches running downward and with 
eighteen openings in all. 
Leaving the squamosal at its hind end on the short shelving 
surface which is overlapped by the extrascapula, the main 
canal passes through a strongly raised portion on the under 
surface of the latter. It then traverses the suprascapula, enter- 
ing it on its upper surface near its lateral edge, where it is 
overlapped by the extrascapula, and leaving it on its under sur- 
face, where it, in turn, overlaps the supraclavicula. Entering 
the supraclavicula on its upper surface at its upper end, it 
passes downward and backward through this bone, leaving it 
on its under surface to enter the first scale of the lateral line 
of the body. 
The extrascapula overlaps the squamosal in front and the 
suprascapula behind, so that the canal only passes through the 
middle third of the bone, giving off trunk 18, with thirty-six 
openings, near its entrance, and trunk 19, with twenty-two open- 
ings, near its exit from the bone. Trunk 20 is given off in the 
suprascapula just as the canal leaves the bone. It runs back- 
ward and outward, and has thirty-nine openings, some of them 
double or triple. Trunk 21, given off soon after the canal 
enters the supraclavicula, runs backward, and, branching once, 
has two openings only at the hind edge of the bone. Trunk 
22, the last one of the cranial system, is also trunk 1 of the 
lateral line. The supraclavicula overlaps the first scale of the 
lateral line, and the double trunk 22-1 is given off at the point 
where the main canal leaves the supraclavicula and turns inward 
to enter the scale. It is a long, open channel on the under sur- 
face of the bone, running downward and backward as a direct 
continuation of the main canal, and having a single large open- 
ing at the hind edge of the bone. 
