The femur belongs to the type specimen which is about 5% larger than the other specimens. This bone is long and rather slender, with the greater trochanter rising well above the head, which is rounded, on a short neck, and has the ligamentary pit on the posterior margin. The thick, rugose, greater trochanter bends in over the head at its upper end. The lesser trochanter is relatively small, and prolonged into a ridge. Unfortunately the third trochanter is broken off in my specimen. The digital fossa is extremely large and deep. Proximally the shaft is flattened, but becomes rounded distally. Just above the condyles there is a deep rugose pit for the plantaris muscle, and on the anterior side the suprapatellar fossa is well marked. The condyles are placed a trifle obliquely; the internal one being shorter and with a rounded articular face, the external condyle being longer, and with a flattened articular face which slopes obliquely inward.
Of the tibia, only the distal end is preserved. This indicates a rather slender bone, with a shallow, fairly wide concavity for the external astragular trochlea, and a narrower and deeper concavity for the internal astragular trochlea. On the internal side of the tibia there is a rugose surface for the fibula.
An isolated lower end of a fibula indicates a slender bone, enlarged distally where it comes in contact with the tibia. The fibula carries on its inner face a moderately large facet for the external side of the astragulus, and on the distal end a wider one for contact with the calcaneum.
The tarsus is compactly built, wider than that of Diadiaphorus, because the external digits are not as much reduced. This especially shows in the greater development of the cuboid and the mesocuneiform, but in other features it is similar to that of its descendant.
Fig. 10. Left pes, dorsal side, ungual phalanx
from specimen No. 3275—½ natural size.
The astragulus is a very characteristic bone. The trochlea is asymetrical, the external condyle rising higher than the internal, and the median groove being wide and shallow. On the nearly vertical outer face of the astragulus, there is a semicircular band-like facet for the fibula. The trochlea extends well around the top of the bone, allowing a wide movement of the foot. The neck of the astragulus is long and wide, carrying a broad flattened head, with its convex facet for the navicular, covering the entire end. On the plantar side are the most marked features. The ectal facet is in two planes, the anterior portion being bent down to nearly right angles with the posterior, which seems to be characteristic of this Diadiaphorus series. The sustentacular facet also is characteristic, being gently rounded and extending clear to the navicular facet on the head, in Diadiaphorus becoming actually confluent with the navicular facet. Just at the edge of this sustentacular facet is a tiny surface where the astragulus rubs on the cuboid, the only case, as far as I am aware, where this occurs in any Litopterna.
Fig. 11. Left astragulus
plantar side:
a, ectal facet—½ natural size;
b, sustentacular facet;
c, facet for cuboid.
The calcaneum is long and slender, the tuber being but slightly enlarged, its sustentacular facet being a broad oval surface, while the ectal facet is in two planes to correspond to that on the astragulus. The facet for the cuboid is at the distal end, but is unusually oblique, its inner margin sloping up almost to the sustentacular facet. It is this slope which brings the cuboid in contact with the astragulus.