| 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.