SCOTT : TOXODONTA OF THE SANTA CRUZ BEDS. 
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and very simple, almost plane transversely and concave palmo-dorsally. 
In Toxodon the magnum is of quite a different shape, being proportion- 
ately shorter proximo-distally and very much broader. The articulations 
are nearly the same as in Nesodon , except that the dorsal portion of the 
lunar facet is less lateral and more proximal and that, when the carpus 
is seen from the front, the facets for the lunar and unciform meet at a very 
obtuse, though distinct angle, while in Nesodon , as above described, they 
form a continuous line. 
The unciform is a very large bone, decidedly the largest of the carpals ; 
it is low and broad and has an irregularly pentagonal dorsal face. The 
proximal end is unequally divided between a narrow surface for the lunar 
and a very broad one for the pyramidal ; the former is oblique, dorsally 
concave, becoming convex toward the palmar side, while the pyramidal 
facet is more proximal and irregularly saddle-shaped. On the radial side 
the unciform extends over the magnum, upon which it rests, and the 
facet for the magnum and that for the lunar meet at an acute angle. 
Below the magnum facet and in nearly the same plane with it, indeed 
continuous with it, is a large, crescentic articular surface for the projection 
from the ulnar side of the head of me. III. On the distal end is the large, 
subquadrate and palmo-dorsally concave facet for me. IV, and on the ulnar 
side is the relatively large, triangular, concave surface for the vestigial 
me. V. In Toxodon the unciform is proportionately broader and more 
massive ; the proximal end is wider than the distal and on the ulnar side 
projects considerably beyond the head of me. IV. The facet for the rudi- 
ment of me. V is relatively smaller than in Nesodon and is displaced 
toward the palmar side. 
The metacarpus consists of three functional members, the second, third 
and fourth and a rudiment of the fifth. The symmetry is nearly, but not 
perfectly mesaxonic, for though me. Ill is symmetrical, me. II and IV do 
not quite form a pair. The three functional metacarpals are quite strongly 
divergent toward the distal ends, almost like the sticks of a fan, caus- 
ing a wide separation of the digits. As was noted above, Ameghino 
believes that a vestige of me. I is also present and in support of this view 
it may be urged that the bone in question does not articulate with the 
scaphoid or trapezoid, but only with me. II. On the other hand, it would 
be most exceptional for the trapezium to be suppressed while any part of 
the pollex remained. 
