Chapter M

Length of centrum ·031
Long diameter of anterior articular face ·024
Long diameter of posterior articular face ·017
Width of neural canal ·019
Height of neural canal ·011
Length of neural spine ·036
Extreme width of sacrum ·052

MEGENCEPHALON.

Megencephalon primævus. _Gen. et spec. nov._

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.

PERISSODACTYLA.

ANCHITHERIUM.

Von Meyer, Jahrbuch für Mineralogie, 1844, p. 298.

Anchitherium ---- ?

A small calcaneum and astragalus of equine type are provisionally referred to this genus until further material enables us to determine them with certainty.

The _astragalus_ has narrow and very oblique condyles, which are more equal in size than in _Orohippus_; the neck is very short, the internal condyle reaching to the face for the navicular; the posterior projection of this condyle is much shorter than in that genus. The articular face for the navicular is quadrate in shape and concave; the cuboid face is very narrow. The articulation with the calcaneum is made by a narrow, convex face. When the two are in position the navicular face of the astragalus is in the same horizontal line as the cuboid face of the calcaneum, thus resembling the arrangement of the horse's tarsus rather than that of _Orohippus_.

The calcaneum is a short, slender bone, having the upper and lower margins convergent toward the tuberosity, and not parallel as in _Orohippus_. The tuberosity is especially small. The face for the cuboid is very narrow.

From the articular facets of these two bones we can see that the tarsus resembled very much that of the modern horse, with a broad, short navicular, and a narrow cuboid. The strata in which these remains were found were somewhat higher than those containing the bones of _Orohippus_.

_Measurements._