The cuboid is large, the external side being longer than the internal. The upper surface is entirely occupied by the facet for the calcaneum, while the lower face is mostly devoted to the facet for Mt. IV, with a narrow streak on the external margin for the vestige of Mt. V. The internal face carries a boss beveled above by the facet for the navicular, and below by the facet for the ectocuneiform.
All the metatarsals are short and heavy as compared with those of Theosodon. Mt. II is compressed above, but enlarges below into a subcylindrical bone, ending in an extensive articular trochlea for the phalanx, the trochlea carrying a carina which extends into the upper surface of the articular area. Proximally, it is so closely approximated to the adjacent metatarsus that these could have had very little independent movement. On the upper internal surface, there is a roughened area, where the endocuneiform overlaps this bone. Mt. III is slightly heavier than the others. On the distal end, its articular trochlea extends well onto the dorsal surface, as does also the carina. Mt. IV is a trifle shorter than the others and stouter. Mt. V is absent but its former presence is indicated by the beveled facet on the cuboid, and by the small roughened surface on Mt. IV.
The phalanges of the third digit are a trifle heavier than those of the other two digits, but of approximately the same lengths. The ungual phalanges were broad compressed hoofs, without traces of clefts.
| Measurements of the Hind Limb | ||
|---|---|---|
| Femur, | length from the head | 177 mm. |
| greatest proximal width | 70 mm. | |
| greatest distal width | 56 mm. | |
| Tibia, | total length | 149 mm. |
| greatest proximal width | 52 mm. | |
| greatest distal width | 56 mm. | |
| Fibula diameter of shaft | 9 mm. | |
| Astragulus, | length | 23 mm. |
| width | 24 mm. | |
| Calcaneum, length | 62 mm. | |
| Metatarsus II, length | 45 mm. | |
| Metatarsus III, length | 48 mm. | |
| Metatarsus IV, length | 42 mm. | |
| Phalanx 1 of digit III, length | 24 mm. | |
| Phalanx 2 of digit III, length | 16 mm. | |
| Phalanx 3 of digit III, length | 17 mm. | |
Fig. 21. (Half tone.) Restoration of Protheosodon coniferus
to show the relatively short limbs, and heavy build as
compared with Theosodon—⅕ natural size.
Restoration
In order to get a comparison of what is known of this form with Theosodon I have outlined a restoration of the animal as a whole, realizing that some essential parts are lacking, but the general proportions can hardly vary greatly from those given. It appears, first, that this form has an unusually short back. Though the limbs and lower jaw are ⅗ the length of those of Theosodon garrettorum, the vertebrae are ½ as long. I have assumed that the number of vertebrae would prove to be the same as in Theosodon. While the limb bones are ⅗ as long as in the Theosodon, they are relatively half again as heavy and with the processes much more developed. The greatest difference is found in the tarsus which is only ⅓ as long as that of Theosodon, though relatively as heavy, and the foot was carried in a nearly plantigrade position the heel raised but a little from the ground, though the anticular ends of the metatarsals and the phalanges indicate that there was a considerable freedom of movement of the various elements. The form seems to be fairly close to the ancestral types such as Lambdaconus of the Casamayor, the limbs of which, however, are entirely unknown, but I should expect that when found these earlier forms would prove to be approximately plantigrade.