In close proximity to the pelvis of the _Uintatherium Leidianum_,
in one of the upper beds we found an intracranial cast, separate
from the bone which had enclosed it, and in such preservation as to
warrant a partial determination, at least, of the type to which it
belonged. Wishing to obtain as full information as the nature of the
cast permitted, we put it in the hands of Dr. Spitzka, of New York,
who kindly undertook an examination, and sent us the following as the
result:
"Sir: The specimen submitted to me is the intracranial cast of
some species of Placental Mammals. The cranium had been subject
to the influences of the atmosphere, etc., for a considerable
period preceding the formation of the cast, and therefore the cast
reflects the sutural dislocations which occurred in consequence.
The base of the brain cast it is not advisable to attempt to
expose, on account of the treacherous nature of the material.
The convolutions corresponding to the internal aspect of the _Os
temporale_ have not been clearly demarcated by the bone surface.
The two narrow eminences on it are casts of the grooves of the
middle meningeal arteries. The convolutions of the occipital
surface had been well marked, but somewhat obliterated through
denudation, etc. The important region bordering on each side of the
median fissure, and corresponding to the fronto-parietal suture, is
unfortunately as good as destroyed; and with this destruction the
key to the interpretation of the specimen is lost. However, this
much can be stated with absolute certainty, that the frontal region
is sufficiently well preserved to state that its convolutions do
not correspond to those of the brain of the tapir, rhinoceros,
hippopotamus, elephant, pig, horse, hyrax, manatus, or any ruminant
or cetacean.
"They also differ in important particulars from those of the
_Canidæ_, differ less from those of the _Felidæ_, still less
from the _Ursidæ_, although corresponding to none of them. The
outline of the cerebral cast is found in two living animals--the
marine otter and the seal. But in the seal the gyri show the
transverse interrupting series of sulci, characteristic of extreme
brachycephaly; and it therefore cannot belong to any animal
corresponding to the seal.
"The sea otter's convolutional details are unknown to me, and I
believe have not yet been studied. I therefore content myself with
stating that the outline of this cast corresponds to the outline of
the sea otter's cranium.
"It would help us a great deal if we could decide the existence or
non-existence of a bony tentorium. The sutures of this cranium, as
far as I can reconstruct them, ran as in the diagram.
"We may state definitely that this was not an ursine, feline, or
canine brain, nor the brain of any terrestrial viverrine. It is
an open question between an _aquatic carnivore_ and an _aquatic
pachyderm_; and although not placing my conclusion on an exact
basis, yet, in view of the general outline, the course of the
convolutions, and the course of the sutures, I incline to the
former view.
"It certainly corresponds to no known brain of a living creature.
In one point I was inclined to suspect it to be a pachyderm,
namely, the decided asymmetry of some of the sulci, but this, by
itself, is not decisive."
"Dr. Spitzka.
"308 East 123d street."
The interesting letter quoted in full above, contains as near a
determination of the character of the animal to which the brain
belonged, as the nature of the cast and the materials for comparison
would permit. In a later report, by means of more complete
comparative material, we hope to be able to reach a more satisfactory
conclusion. However, as Dr. Spitzka writes, the _general outline_,
the _course_ of the _convolutions_, and the _line_ of the _sutures_
offer strong presumptive evidence that the cast belongs to one
of the _Aquatic carnivores_. Not far from the brain was found a
sacrum, which is described above as belonging to some carnivore,
though further determination was impossible. Whether there was any
connection between the two is difficult to state. The presence of
an aquatic carnivore in the Bridger eocene is new to science; but,
aside from this, the brain is of a much higher order than previous
discoveries would lead us to expect in such an early formation.
Professor Marsh's researches have led him to form the opinion that
the eocene mammals had brains of a low character; but this specimen
shows that this is not true of all, if it is of most of them. The
convolutions are not only numerous and well marked, but they are
complicated, showing the transverse as well as the longitudinal
folds. To such an extent is this true that the brain will bear
comparison with the very highest modern carnivorous types.
We hope to be able to give further notes upon this interesting
specimen at a later date.