Читать книгу Palæontological Report of the Princeton Scientific Expedition of 1877 - Francis Speir - Страница 6
PERISSODACTYLA.
ОглавлениеANCHITHERIUM.
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.
TIBIA.
| Upper Jaw. | M. |
| Length | ·178 |
| Width of proximal surfaces (transverse) | ·032 |
| Width of proximal surfaces (antero-posterior) | ·019 |
| Transverse diameter of shaft | ·022 |
| Antero-posterior diameter of distal articulation | ·018 |
| Transverse diameter of distal articulation | ·018 |
The tarsus.—The astragalus (Plate IX., Fig. 5) has the condyles asymmetrical and divided by a deep groove; the head is narrow, with the neck elongate. The face for the cuboid is small, and confined to the external border.
The calcaneum (Plate IX., Fig. 4) is long and compressed, with its upper and lower margins straight and nearly parallel; its tuberosity is large. The face for the cuboid is small.
The navicular (Plate IX., Fig. 6) is proportionately longer and narrower than it is in the modern horse. The internal and middle cuneiforms were probably separate.
Metatarsals (Plate IX., Fig. 7).—Three in number. Are very much shorter proportionately than in the modern horse. In shape they are compressed and arched forward. The distal ends are flattened vertically, arched forward, and deeply grooved in the middle.
The phalanges (Plate IX., Fig. 7) are very short, rather stout, and very smooth and convex above.
The ungual phalanges are very thin and crescent shaped.
Measurements.
ASTRAGALUS.
| M. | |
| Greatest width | ·029 |
| Greatest length | ·022 |
| Length of navicular facet | ·017 |
| Width of navicular facet | ·012 |
| Length of tibial trochleæ externally | ·016 |
CALCANEUM.
| M. | |
| Total length | ·058 |
| Total width | ·019 |
| Depth in front | ·022 |
| Length of heel | ·035 |
| Depth of heel | ·018 |
| Length of cuboid facet | ·014 |
NAVICULAR.
| M. | |
| Width | ·009 |
| Length | ·010 |
PHALANGES.
| M. | |
| Length of first phalanx | ·022 |
| Width of first phalanx | ·012 |
| Length of second phalanx | ·013 |
| Width of second phalanx | ·010 |
| Length of ungual phalanx | ·005 |
| Width of ungual phalanx | ·010 |
PALÆOSYOPS, Leidy.
