38 THE DESEADO FORMATION OF PATAGONIA 
navicular, and a shallow saddle-like one below for Mt. 
II, which is entirely carried by this bone. 
The ectocuneiform is considerably larger than the meso- 
cuneiform, resting above on the navicular, and carrying 
below the whole of Mt. III. On its inner side are two 
facets which rub against the upper end of Mt. II. 
The cuboid is a nodular bone, its upper surface occupied 
by the facet for the caleaneum, the lower face occupied by 
the facet for Mt. IV, while on the external side 
there is a tiny beveled facet for the vestige of 
Mt. V, and with a small boss on the inner 
ae surface which carries two tiny facets, the upper 
Fig. 12. Cuboid One for the ectocuneiform and the lower for the 
internal side to 
show: a, facet yavicular. On this same inner side, near the 
for astragulus ; 
b, upper facet top there is a second small boss, which carries 
for navicular; c, 
facet for calcay- 
nam d, loo @ tiny facet to rub on the astragulus;"amd 
list! eiacctioe below that a second tiny facet for the navicular. 
ert aaegal The pes consists of three digits, with a vestige 
a” of Mt. V. Of the developed digits, the median 
one is the largest, but the two lateral digits are only a little 
smaller and were functional, so that this form was_ truly 
three-toed, comparable in the digital reduction to Meso- 
hippus. 
Mt. II is flattened above but soon broadens into a 
rounded shaft of considerable length, on the end of which 
is the articular trochlea, with the carina extending onto 
both the upper and lower surface, being, however, higher 
on the lower surface. Proximally this bone is overlapped 
by the endocuneiform, is carried by the small mesocunei- 
form, and also articulates on the inner side of the ecto- 
cuneiform. Mt. III is also compressed at the upper end, 
broadens below, and carries an articular trochlea similar 
to that of Mt. II, except that the carina does not extend 
so far onto the upper surface. Like Mt. II, Mt. IV is 
carried high on the tarsus, and therefore, though nearly as 
long as Mt. III, it does not have the same effective length. 
