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._
M.
Greatest length of astragalus 0·021
Greatest breadth of ditto ·018
Length of neck of ditto ·005
Width between the condyles ·010
Vertical diameter of face for navicular ·012
Transverse diameter of ditto ·012
Length of calcaneum ·046
Width of face for cuboid ·006
From Henry's Fork.
OROHIPPUS, Marsh.
Am. Jour. Sc. vol iv., p. 207, third series.
_Generic Characteristics._--"The crowns of the upper true molars
are composed of a pair of external cusps similar to those of
anchitherium. There are two corresponding inner tubercles, from
which ridges extend obliquely to the anterior inner margin of the
outer cusps; but the anterior ridge is divided so as to form an
intermediate anterior tubercle. All the teeth preserved have a
distinct basal ridge."
_Species Known._--
Orohippus pumilus, Marsh.
Orohippus major, Marsh.
Orohippus agilis, Marsh.
Orohippus gracilis, Marsh.
Orohippus pumilus? Marsh.
Specimen obtained. Penultimate and third superior molars, with part
of zygoma.
From Cottonwood Creek.
Orohippus major? Marsh.
_Femur_ (Plate IX., Fig. 1).--The femur has a small, nearly
hemispherical head, developed on a long and slender neck; the head is
but slightly out of the axis of the shaft, and has a large pit for
ligamentous insertion. The shaft is long, simple, and curved slightly
forward. At the proximal end it is broad and flattened axially; below
this it becomes expanded fore-and-aft, but it thickens greatly at
the distal end, just above the condyles. The great trochanter is
large and retroverted, rising above the head, with two prominences
rising from it, one on top, the other back. The digital fossa is
wide and deep, penetrating far into the great trochanter. The second
trochanter is a small rounded ridge; the third trochanter is large
and prominent, curving slightly forward. The condyles are long and
narrow, projecting very far back, and are separated by a wide and
deep popliteal groove. From the external condyle a low ridge runs
obliquely, forming the upper border of the shallow popliteal space.
The trochleæ are long, very convex, deeply grooved, and symmetrical.
_Measurements of Femur._
M.
Width between head and great trochanter ·019
Width at third trochanter ·034
Diameter of head ·019
Width at condyles ·028
Width of trochlea ·015
Height of great trochanter ·015
Diameter fore-and-aft of shaft at middle ·018
The _tibia_ (Plate IX., Fig. 3) is very long and heavy, with broad
proximal articular face, the inner borders of which are prolonged
upward and separated by a groove.
The shaft at the tuberosity is subtriangular, with strongly concave
sides. The tuberosity is prominent, with a deep pit on its upper
surface for the insertion of the ligament of the patella. The shaft
below becomes sub-cylindrical, and decreases regularly in size
downward. Its curvature is forward. The distal articular face is
divided by a smooth ridge into two deep facets. The malleolus is long.
The _fibula_ (Plate IX., Fig. 2) is distinct, straight, and very
slender. The distal end is but slightly expanded, and is strongly
marked by a vertical groove externally. The proximal end articulates
with the overhanging portion of the proximal face of the tibia.
_Measurements of Tibia._