470 ALLIS: [Vou. II. 
Course of the Canals. 
In tracing the canals through the dermal bones, the method 
used was the following. The head of a fish was boiled a few 
minutes, cleaned as much as possible, and then allowed to 
macerate until the tissues were thoroughly softened. The dif- 
ferent bones that contained any part of the canals of the lateral 
system were then separated and carefully cleaned, the outside 
with a brush, and the canals by forcing water through them 
with a pipette. They were then heated in water and injected 
with a blue gelatine solution, and after a short exposure to the 
air, to allow the gelatine to set, cleaned and put in 50 per cent 
alcohol. The smaller tubes of the system, that the gelatine 
mass had failed to penetrate, were filled by forcing with a 
needle little plugs of the cold injection mass into them from 
the openings on the surface. Finally, the bones were scraped 
on the inner surface below the canals, until under the micro- 
scope every branch could be distinctly traced. In bones that 
had been simply macerated without boiling, the canals and 
branches were so filled with a chalk-like deposit that they could 
not be successfully injected. 
All the dermal bones containing any part of the canals of the 
lateral system are shown in Figs. 40-43, Pl. XL. They are 
enlarged two diameters, and all, excepting the suprascapula and 
supraclavicula, placed in serial order as they occur in the fish. 
In these figures the canals and dendritic systems lying in the 
dermal tissues between the frontal and nasal, and at either end 
of the pre-operculum, are shown, as well as all the ramifications 
of the osseous canals, and the openings and channelled lines on 
the outer surfaces of the bones. In Figs. 45, 46, and 47, Pl. 
XLI., three views are given of the skull, natural size, with the 
dermal bones in place. In Figs. 46 and 47 the canals are, for 
fuller illustration, shown’ on both sides of the head, but the 
dissections were made on one side only, and the perfect bilateral 
symmetry shown in the drawing does not exist in nature. 
The arrangement of the canals and dendritic systems shown 
in these figures is the normal one, from which there are, how- 
ever, frequent variations. There are on each side of the head 
the three well-known canals: the infra-orbital, supra-orbital, and 
operculo-mandibular, and in addition a supratemporal or occipital 
cross-commissure. 
