Chapter 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._