2l6 
PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 
rated from the surface for the navicular, which, owing to the obliquity of 
the neck, it touches near the fibular border, while in Nesodon it becomes 
confluent with the navicular facet near the tibial border. The navicular 
facet itself is relatively narrower and of more quadrate outline in 
A dinotherium. 
The calcaneum has a somewhat more elongate, slender and laterally 
compressed tuber than in Nesodon, with a more nearly straight plantar 
border ; the fibular facet is shorter proximo-distally, but more prominent 
and rises more abruptly from the dorsal side, and the external facet for the 
astragalus is less oblique and is not extended so far upon the tuber. The 
sustentaculum is less produced proximo-distally and its two diameters 
are more nearly equal ; it is also relatively thinner planto-dorsally and has 
a deeper and better defined sulcus on the plantar face. The distal facet 
for the cuboid is rather more concave. Ameghino, who has given a very 
full comparison of the calcaneum and astragalus of Adinotherium and 
Nesodon, says of them: “Ces differences dans la forme du calcaneum et 
de l’astragale sont aussi importantes que celles qui existent entre les 
memes os des Paleoth£res et des chevaux, animaux qui Ton place dans 
deux families differentes” (’94/, 243). In my judgment, however, this 
greatly overstates the importance of the differences above described. 
These differences are merely such as one would expect to find between 
a relatively large and heavy animal and a small and light one of the same 
group. 
The remaining elements of the tarsus in Adinotherium are less differ- 
ent from those of Nesodon than are the calcaneum and astragalus. The 
navicular and cuboid differ hardly at all in shape and proportions from those 
of the latter, but the plantar hook of the navicular is even more reduced 
and on the cuboid also this hook is very inconspicuous, and the proximal 
surface of the cuboid for the calcaneum is somewhat more convex. The 
ento- and mesocuneiforms are ankylosed and the compound bone agrees 
in every respect, save size, with that of Nesodon , but the ectocuneiform 
differs in several details. It is relatively narrower and slightly higher 
proximo-distally and contracts more rapidly toward the plantar side ; the 
proximal facet for the navicular is more nearly concave and the facet on 
the fibular side for the cuboid is much more extended planto-dorsally. 
The metatarsals are very much smaller than the metacarpals and show 
the same lack of symmetry as in Nesodon . Metatarsal II is the shortest 
