scott: toxodonta OF THE SANTA CRUZ beds. 
175 
relatively shorter and much broader than in the pes and has a more con- 
cave proximal surface and a similarly saddle-shaped distal trochlea, which 
is likewise more concave transversely. 
When the phalanges of the fourth digit of the pes are put together and 
in connection with the metatarsal, it is seen that they curve toward the 
median line in a peculiar and characteristic fashion, which is better shown 
in Sinclair’s figure (see p. 8, text-fig. 4, B) than in PI. XXV, fig. 9, 
because in the latter the phalanges are drawn as separated from one 
another. In this digit the phalanges resemble those of digit II in form, 
but are considerably larger and somewhat asymmetrical. The distal 
trochlea of the first phalanx is much more oblique to the long axis of the 
bone than in digit II or III and is slightly reflected upon the dorsal face, 
which is not true of the other digits. The ungual is relatively shorter 
and heavier than in digit II and has a more truncate free border, but is 
otherwise similar in form. 
I have before me only the second phalanx of digit IV in the fore foot 
and this, except for its larger size, is closely similar to the corresponding 
bone in the pes, but is not of itself sufficient to show whether the pha- 
langes of this digit had the same medial curvature as in the pes, or not. 
In both fore and hind foot a long and narrow sesamoid is attached to the 
metapodials on each side of the distal carina, but there appears to have 
been none between the second and third phalanges. 
In Toxodon the pes has undergone some remarkable modifications, 
most of which are obviously due to the great increase in the size and 
weight of the animal. The astragalus has an even more flattened trochlea 
than in Nesodon and a somewhat longer and more obliquely directed 
neck and, on the fibular side, the trochlea projects over and rests upon 
the distal end of the calcaneum, an additional articulation of an altogether 
exceptional character, though perhaps an incipient stage of it is present in 
Nesodon. The tuber calcis is very broad and massive, while the portion 
of the calcaneum distal to the fibular facet is very short ; the fibular facet 
itself is very large, though not so prominent as in the Santa Cruz genus. 
A very extraordinary feature of this calcaneum is the position of the cuboid 
facet , which is on the plantar side , at right angles to its normal position ; 
the tuber thus projects directly backward, nearly at a right angle with the 
long axis of the foot. No indication of this most unusual arrangement 
is to be seen in Nesodon, in which the calcaneo-cuboid articulation is of 
