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PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
In Toxodon the fore-arm bones are relatively shorter and very much 
more massive than in Nesodon, though of similar construction. The dis- 
proportion between the ulna and radius is even greater than in the Santa 
Cruz genus, the ulna having increased in thickness and weight more than 
the radius. The radius resembles that of Nesodon in form, but is pro- 
portionately shorter and stouter ; the distal end is especially massive and 
the scaphoid facet emarginates the dorsal border more deeply and in a 
more conspicuous way. The ulna is extraordinarily heavy ; the olecranon 
projects much more strongly behind the plane of the shaft and is far thicker 
at the free end than in Nesodon. The sigmoid notch is much the same in 
both genera, but the short shaft in Toxodon is not only very much heavier, 
but has acquired a subquadrate shape, somewhat as in the Proboscidea. 
The styloid process is relatively decidedly shorter than in Nesodon and 
is displaced to the extreme outer side of the distal end, which extends 
far internally, or radially, from it and thus gives quite a different 
appearance to the distal end. 
The manus (Pis. XXII, fig. 5 ; XXVI, figs. 4-6) is surprisingly small 
and weak in proportion to the size and weight of the animal. The 
carpus is very broad transversely and short proximo-distally and is 
already of completely interlocking type, as much so as in the Perisso- 
dactyla, the scaphoid articulating extensively with the magnum and the 
lunar resting almost equally upon the magnum and unciform. Aside 
from its much smaller size and lighter construction, this carpus is very 
similar to that of Toxodon , though there are many differences of detail, 
no doubt due to the readjustment necessitated by the greatly increased 
size and weight of the Pampean genus. 
The scaphoid is low, broad and irregular in form ; the dorsal face has 
the shape of an irregular, inverted and truncated triangle, broad proximally 
and narrowing distally ; the palmar face is narrow, strongly convex and 
rugose. Proximally, the articular surface for the radius is almost plane 
transversely and is made slightly concave palmo-dorsally by the elevation 
of the posterior or palmar border ; the whole proximal end is not covered 
by the radial facet, but a broad, rugose area extends around the palmar 
and internal sides. On the ulnar side is a facet for the lunar, which is 
continuous with that for the radius ; this lunar surface is very narrow 
proximo-distally, but extends for nearly the whole dorso-palmar diameter 
of the scaphoid and is slightly convex in that dimension. This is the 
