Sinclair: typotheria of the santa cruz beds. 
8i 
astragalus on the dorsal surface of the navicular. At the proximal inter- 
nal extremity a strong tubercle is developed, as in all the Santa Cruz 
Typotheria. The most striking difference by which the navicular of 
Hegetotherium may be differentiated from the corresponding element in 
Protypotherium is in the large size and characteristic shape of the meso- 
cuneiform facet. 
The cuboid is much longer than in Protypotherium , but the calcaneal 
facet is smaller. Distally, it supports a large concavity common to the 
fourth and fifth metatarsals. Proximally, there is a single oval facet for 
the calcaneum, convex in dorso-plantar section and slightly concave trans- 
versely. Internally, there are a large, oval, almost plane surface for the 
navicular, two small, oval, approximately plane surfaces for contact with 
the external cuneiform, and a small crescentic, plane facet for the third 
metatarsal. The plantar surface supports a heavy tubercle overhanging 
the peroneal groove. 
The inner cuneiform is an elongated, scale-like element, articulating 
proximally with the navicular and applied to the inner side of the meso- 
cuneiform and the second metatarsal. The mesocuneiform is unknown. 
The outer cuneiform differs greatly from that of Protypotherium in the 
extent of its articulation with the second metatarsal. Proximally, it sup- 
ports an almost plane, oval surface for the navicular ; distally, a dumb- 
bell-shaped facet concave in both diameters for the head of the third 
metatarsal ; on the outer side, two small, oval facets for the cuboid and 
internally, three facets, a large oval facet, deeply concave proximo-distally, 
for articulation dorsally with the head of the second metatarsal, a circular 
plantar facet, concave in proximo-distal section and plane transversely, for 
the plantar process of the same metatarsal, and a narrow, B-shaped surface 
for the mesocuneiform. The plantar surface supports a prominent, pedun- 
culate knob. 
The metatarsus is tetradactyl, the axis of the foot passing through the 
third digit, which is much the longest. The first digit is entirely wanting ; 
the second and third are large, the third exceeding the second in length ; 
the fourth is much smaller and the fifth greatly reduced, but supporting 
phalanges. Proximally, the metatarsals overlap, the amount of imbrica- 
tion increasing toward the inner side of the foot, until the second attains 
the extreme degree of overlap on the outer cuneiform just described. 
Proximally, the articulations between the third and fourth metatarsals 
