scott: toxodonta OF THE SANTA CRUZ beds. 
173 
facets for mt. IV, a large, deeply concave pit near the dorsal border and 
a much smaller, nearly plane surface on the plantar extension of the head. 
The shaft is short and heavy, broad and much compressed planto-dor- 
sally, widening distally. A slight degree of asymmetry is shown in the 
difference between the two lateral borders of the shaft, that on the tibial 
side being straight, while the fibular border is slightly concave. In 
the same way, the tuberosity above the pit for the lateral ligament is 
distinctly more prominent on the fibular than on the tibial side. The 
trochlea, which is low and wide, is strongly compressed planto-dorsally 
and the carina, though inconspicuous, is yet more prominent than that of 
mt. II. 
Metatarsal IV is nearly as long as mt. Ill and heavier, and is some- 
what longer and decidedly stouter than mt. II. The proximal end has a 
large, nearly plane surface for the cuboid, which is somewhat pear-shaped, 
contracting toward the postero-internal angle. On the tibial side of the 
head, near the dorsal border, is a very prominent convexity, which fits 
into the concavity on the fibular side of mt. Ill, already described ; the 
other facet for mt. Ill near the plantar side is very much smaller and 
slightly concave ; these two facets are separated by a deep sulcus. The 
shaft is rather narrow, but thicker planto-dorsally than that of mt. Ill 
and having a more rounded dorsal face ; the tibial border is nearly 
straight, while the fibular border is quite strongly concave. This form 
of asymmetry and the broader, heavier shaft distinguish this metatarsal 
decidedly from mt. II, of which it is not so nearly a counterpart as it is 
in the Perissodactyla. The tuberosity on the fibular side of the distal end 
is much larger and more prominent than that on the tibial side. The 
distal trochlea is much broader and more symmetrical, but lower, than 
that of mt. II, and the carina, which divides the plantar side of the 
trochlea into a broader and more concave external portion and a narrow, 
flatter internal part, is more distinct. 
The phalanges of the three digits are all different from one another ; 
those of digit III are the largest and those of digit II much the smallest 
of the series, as is also true of the manus, though the phalanges of each 
digit of the latter are considerably larger than those of the corresponding 
digit of the pes. In the hind foot the first phalanx of digit II is short, 
narrow and thick planto-dorsally and nearly symmetrical in form. The 
proximal surface, for articulation with the metatarsal trochlea, is slightly 
