94 
PATAGONIAN EXPEDITIONS ! PALAEONTOLOGY. 
natural positions. Here also, correspondence with Hegetotherium is ex- 
ceedingly close. The astragalar trochlea (PI. X, fig. 15) is wide, shallow 
and bilaterally symmetrical, with the outer crest sharper and higher than 
the inner. The trochlear surface is confined to the dorsal aspect of the 
bone, but is not produced as far backward as in Protypotherium. The 
shallowness of the trochlea and its small posterior extension suggest a 
plantigrade position for the foot as indicated in the restoration (PI. XI). 
The proximal and distal corners of the astragalar body on the inner and 
outer sides respectively are prolonged as in Hegetotherium. The fibular 
facet is a vertical crescentic plane surface ; that for the internal malleolus 
a convex surface sloping inward. The neck is long and obliquely directed 
toward the inner side of the foot, and the head hemispherical. The cal- 
caneum is almost a replica on a smaller scale of that of Hegetotherium , 
the shape and arrangement of the facets being practically the same in each 
(see description p. 80 and Pis. II, fig. 15, X, fig. 27). Slight differences 
appear in the top-shaped rather than circular sustentacular facet, the more 
oblique position of the navicular facet and the slightly shorter and more 
convex astragalar facet in Pachyrukhos as compared with Hegetotherium. 
The tarsals have not been disturbed from their original position in No. 
9481 of the American Museum collection (PI. X, fig. 15) and, so far as 
it is possible from the type of mounting employed, to compare them, they 
are exactly the same in shape and position as in the last named genus 
(pages 80, 81 and Pis. II, fig. 19, X, fig. 15). No trace of a hallux remains. 
The inner cuneiform, although not present, seems, from its articular sur- 
faces, to have been scale-like as in Hegetotherium. The metatarsals inter- 
lock strongly proximally, the second articulating with the middle of the 
outer cuneiform and the third with the cuboid. The second and third are 
the most robust, the latter exceeding the former in length. The fourth is 
more slender than the second and slightly shorter, and the fifth quite 
slender and shorter than the fourth. Well developed keels are present 
on the plantar surfaces. The phalanges closely resemble those of the 
fore foot, differing only in size and greater robustness. Their natural 
position is probably more strongly angulate than is represented in the 
restoration (PI. XI). The terminal phalanges (PI. X, fig. 15) are trans- 
versely expanded distally as minute hoofs without trace of median cleft. 
Restoration (PI. XI). — The restored skeleton shows effectively the 
much greater length and strength of the hind limb as compared with the 
