64 
branch of the main canal traverses first the prefrontal bone, and then 
the postorbital and following bones of the circumorbital series, thus 
having a somewhat peculiar course. 
In Psepherus gladius, CoLLInGE (No. 12, p. 519) finds much the 
same conditions as in Acipenser, the supratemporal commissure leav- 
ing the main canal in the epiotic and traversing a median dermo- 
occipital. In very large specimens he says that it traverses also the 
hind end of the parietal, a statement that certainly needs confirmation 
and explanation. 
All these Ganoids thus agree in that the so-called supratemporal 
crosscommissure of the lateral canal system traverses bones that are 
of purely dermal origin; and in that these bones in no way enclose or 
protect, or have any direct relation whatever to, the semicircular 
canals of the ear. They are accordingly not true otic bones in any 
sense of the word, and this is further indicated by the separate and 
independent development of true otic bones in all three of the bony 
Ganoids described. In Teleosts, also, the commissure traverses dermal 
bones that are wholly unconnected with true, primary, otic components. 
In Teleosts and the three bony Ganoids, the commissure traverses no 
median bone. In the cartilaginous Ganoids it is said to traverse such 
a bone. There is thus a difference here that may be important, and 
the development of the bones concerned, and of the canal they lodge, 
deserves careful investigation, more especially as the vexed question 
of the supraoccipital bone is here apparently directly concerned. 
According to SAGEMEHL (No. 29, p. 519) a supraoccipital bone 
is found in all Teleosts, but is wanting in all Dipnoids, and in all Ganoids. 
The bone, according to him, was never possessed by the Ganoids, and 
is, in Teleosts, a recent acquisition to the skull. In Acipenser and 
Polyodon, he says no trace of it is found, the most anterior, median, 
dorsal “Hautschild” lying, according to him, posterior to the cross- 
commissure of the lateral canal system. The bone can not, accordingly, 
be derived, according to him, from a dermal ossification, and he looks 
for the cause of its origin in the assimilation of certain vertebrae in 
the occipital region of the skull. His own words are: “Nach meiner 
Ansicht giebt der Processus spinosus, indem er sich an die knorpelige 
Spina occipitis anlegt, die Veranlassung zur Entstehung einer zuerst 
periostalen Ossification an dieser Stelle, die jedoch bald Beziehungen 
zur knorpeligen Unterlage gewinnt und, sich der Gestaltung der letzteren 
anpassend, das Occipitale superius hervorgehen läßt.” The assimil- 
ation of the oceipital vertebrae is then said to be indicated by the 
occipital nerves of the animal. These nerves are said to be wholly 
wanting in Amphibia, and a supraoccipital bone is accordingly wanting, 
