16 ON THE STRUCTURE OF EUSTHENOPTERON 
represents in part the parasphenoid of other ganoids and of tele- 
osts. That this is true is proved by the fact that its ventral mar- 
gin is studded with minute denticles. That it terminated just 
below the junction of the frontals and parietals is positively dem- 
onstrated by many specimens in the Buffalo Museum in which all 
the parts are preserved in their natural relation to each other and 
in which the delicate bones comprising the brain case are hardly 
crushed or distorted. It includes, however, the whole spheneth- 
moid (ethmoid and orbitosphenoid) region, although I have been 
unable positively to make out any sutures; and the upper walls 
form the front part of the brain case. 
In this connection I shall quote from a letter from Dr. William 
H. Gregory to whom I am greatly indebted for advice: “The pro- 
found differences from Polypterus are very surprising. Possibly 
they may indicate merely that Polypterus has become ichthyized 
or converged toward normal fish-like conditions in the millions of 
years since the upper Devonian. It may well be that the back- 
ward extension of the parasphenoid so as to cover the back part 
of the skull base is in some way correlated with the peculiar spec- 
ialization of the eye muscles which builds up the myodome or 
muscle canal in modern fishes. Assuredly this condition must be 
a secondary one because it traverses the region formerly occupied 
by the connection between the hypophysis and the base of the 
brain, and secondly because the parasphenoid is a dermal element 
representing a part of the stomadaeum or in-pushing of surface 
tissue. Your fish would then represent a stage in which this in- 
pushing in the mid-line had not yet extended behind the infundi- 
bulum-hypophysis, while the denticulate tract of the pterygoid and 
ectopterygoid shows that at the sides this in-pushing had extended 
backgnearlyntoytnenquadrate sma eee This stage must have 
been passed through by the earlier fishes, but whoever dreamed 
of finding it in a real specimen?” 
Dr. Sagemehl (1883) in his discussion of the cranium of Amia 
remarks that in ganoids and dipoans the parasphenoid does not 
terminate at the base of the true skull but extends backward be- 
neath several vertebrae—as many as seven or eight in Polypterus 
—and thinks that this must have been also the case in the direct 
ancestors of the existing bony ganoids and teleosts; and that in 
later times a curtailment from behind took place causing a reduc- 
tion in number and consolidation of the vertebra resting upon this 
