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PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
Cruz and the Pampean genus, not only in innumerable matters of detail, but 
also in the general proportions and whole appearance of the two animals. 
Toxodon is a far larger and, in particular, a much more massive animal and 
all the bones of its skeleton are very much heavier, not only actually, but 
proportionately as well. A very peculiar appearance is given to the skele- 
ton by the relative shortness of the fore-legs, depressing the whole anterior 
portion of the vertebral column and bringing the head much below the level 
of the back and loins. This peculiarity is especially striking and remark- 
able when the skeleton is seen from the front end. Something of the same 
sort is to be seen in Nesodon , but in no such pronounced degree, and this 
constitutes one of the principal differences in the appearance of the two 
skeletons. 
In Toxodon the skull is relatively longer and shallower dorso-ventrally 
and tapers more to the anterior end ; several minor modifications combine 
to alter its appearance very materially. Of these may be mentioned the 
more elevated orbits, the much shortened nasals, with the more elongated 
and sloping anterior nares, the more prominent crest on the dorsal side 
of the premaxillaries, and the long diastema behind the functional incisors. 
Even more characteristic is the shape of the mandible, which, with its com- 
pletely procumbent incisors, depressed and flattened chin, broad and shal- 
low symphysis, and very high, narrow ascending ramus, differs widely 
from that of Nesodon. The neck is relatively short and heavy, and has much 
less prominent spines than those of the Santa Cruz genus, while in the 
anterior thoracic region the spines are far higher and heavier and form a 
more prominent shoulder-hump. In the remainder of the thoracic and 
the lumbar regions the spines are lower, broader and more plate-like and 
all have a backward inclination, much as in the Proboscidea. The trunk 
is relatively shorter, not only having one or two less vertebrae, but the 
centra of most of the trunk-vertebrae are proportionately shorter and much 
heavier. The backbone, disregarding the spines, forms a regular arch, 
curving upward from the neck to the loins. The ribs are very long and 
broad and are strongly curved outward, forming a very capacious thorax. 
The sternum has quite a different appearance from that of Nesodon , owing 
to the depressed form of the manubrium, though the two are fundamen- 
tally similar. 
The scapula has proportions altogether different from that of the Santa 
Cruz genus, being much longer proximo-distally and narrower transversely. 
