scott: toxodonta OF THE SANTA CRUZ beds. 
149 
dorsal and ventral sides. The transverse processes are long, broad and 
depressed and extend straight out from the sides of the neural arch, with- 
out anterior or downward curvature, except on the last vertebra, which 
has quite peculiar transverse processes ; they are narrow and thick at the 
base, becoming wider and thinner toward the extremities and with a con- 
cave anterior border, which gives an appearance of a forward curvature ; 
on the posterior border of each process is a small facet for articulation 
with corresponding facets on the sacrum. The zygapophyses are of the 
cylindrical, interlocking kind, found in the Litopterna and Artiodactyla, 
the posterior pair being convex and the anterior strongly concave. From 
the outer margin of the latter arise the metapophyses, which are much 
more prominent than in the thoracic region. The neural canal remains 
small and the pedicles of the arch are not perforated for the nerves, which 
pass out through deep and narrow slits. The neural spines are rather 
short and weak and have a slight forward inclination. 
So far as I am aware, no sacral or caudal vertebrae of Nesodon have yet 
been found, but the sacrum is known in the very closely allied genus, 
Adinotherium, in which it consists of six vertebrae and the centrum of the 
last one is so large as to make it very probable that the tail was moder- 
ately elongate and stout. There is every reason to assume that the rela- 
tions were similar in Nesodon. 
The trunk-vertebrae of Toxodon differ in a number of details from those 
of Nesodon , differences which are for the most part referable to the greatly 
increased size and body weight of the Pampean genus. The vertebrae are 
of nearly the same relative length as in the Santa Cruz genus, but 
are much more massive. The first thoracic has a much shorter and more 
slender spine, but those of the four succeeding vertebrae are far longer and 
heavier than in Nesodon and the descent from them to the middle region 
is much more abrupt, making the hump at the shoulders far more promi- 
nent and conspicuous. In the posterior thoracic and lumbar regions the 
spines are low, but very broad antero-posteriorly and have greatly thick- 
ened and very rugose tips. All the neural spines of the trunk-vertebrae 
have a backward inclination, somewhat as in the Proboscidea, although 
chose of the last three thoracics are nearly erect. Throughout, the 
transverse processes are relatively shorter and the metapophyses some- 
what less prominent than in Nesodon. 
The ribs of Nesodon are not especially characteristic, but resemble those 
