172 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
The ectocuneiform is very much larger and has much the same shape 
as in the perissodactyls, other than the horses. Its proximal surface meets 
that of the mesocuneiform at an open angle, the two bones together form- 
ing a shallow depression, into which the navicular fits. On the fibular 
side, in addition to the facets for the mesocuneiform already described, 
are two quite large and widely separated ones for the head of mt. II, of 
which that near the dorsal border is of complex shape, convex distally and 
concave proximally, while that near the plantar border is plane. On the 
fibular side is a large plane surface for the cuboid and the distal end is 
covered by the very large facet for mt. III. 
The cuboid is very short proximo-distally, but broad, thick and heavy ; 
it has no plantar hook, merely a low rugosity. There are four articular 
surfaces, a large, saddle-shaped, proximal one for the calcaneum ; an 
almost equally large, plane facet on the distal end for mt. IV, and on 
the tibial side an obliquely proximal surface for the navicular and, below 
this, a large, plane, lateral surface for the ectocuneiform. 
The metatarsus consists of three members, without any remaining ves- 
tiges of mt. I or V. The metatarsals are so arranged as to be strongly 
divergent distally, as is also the case in the metacarpals, and the mes- 
axonic symmetry is less complete than in the manus, since digits II and 
IV do not form an entirely symmetrical pair and even the symmetry of 
digit III is not perfect. Metatarsal II is the shortest and lightest of the 
series ; the head is narrow, but thick planto-dorsally and bears a trans- 
versely concave facet for the mesocuneiform, and on the tibial side is a 
small oblique surface for the entocuneiform, the head appearing to notch the 
compound cuneiform in a very characteristic way. This metatarsal rises 
above the head of mt. Ill and abuts laterally against the ectocuneiform, 
with which it articulates by means of two large facets, but no distinct sur- 
face for mt. Ill is visible. The shaft is stout and of trihedral section, 
becoming broad and more flattened toward the distal end. The trochlea 
is rather oblique and asymmetrical and the carina is very low and incon- 
spicuous. 
Metatarsal III is somewhat longer and much heavier than mt. II ; the 
head bears an oblique facet for the ectocuneiform, which is convex planto- 
dorsally and is incompletely divided by a constriction from each side into 
a larger dorsal and smaller plantar portion ; the latter is wider than the 
corresponding surface on the ectocuneiform. On the fibular side are two 
