SCOTT: TOXODONTA OF THE SANTA CRUZ BEDS. 
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of the lumbar vertebrae the spinal nerves pass out through deep and 
narrow notches, which emarginate the pedicles of the neural arch. 
The sacrum (PI. XXVI, fig. 1) resembles that of Toxodon on a very 
small scale, but is relatively longer and has one additional vertebra, six 
instead of five. The centra are broad and much depressed and that of 
the last vertebra is so large as to indicate a well developed tail, which 
was probably proportionately longer and more slender than in the Pam- 
pean genus. The surfaces for the attachment of the ilia are remarkably 
small, though relatively as large as in Toxodon , and, as in that genus, 
are formed almost entirely by the pleurapophyses of the second sacral. 
The transverse processes of the succeeding vertebrae are fused into a 
broad, very thin plate on each side, perforated by the foramina for the 
spinal nerves, which are relatively much smaller and less conspicuous 
than in Toxodon. In the latter the last sacral has on each transverse 
process a facet for articulation with the first caudal, but in Adinotherium 
the first caudal seems to be fused with the sacrum. The prezygapophyses 
of the first sacral are prominent and functional and bear well defined 
metapophyses ; those of the succeeding vertebrae are vestigial, but less 
reduced than in Toxodon. At the anterior end of the sacrum the neural 
canal is broad, but very low and depressed, and at the posterior end it is 
very small and nearly circular, the relative size of the canal being much 
the same as in Toxodon. The degree to which the neural spines of the 
sacrum are fused into a ridge differs in various specimens, though the 
material is insufficient to show whether the difference is specific or indi- 
vidual, or merely a matter of age. The spines of the first and last sacrals 
are isolated, while those of the intermediate vertebrae are ankylosed for 
more or less of their height, but the tips are always free. In Toxodon 
only the first spine is separate ; all the others are indistinguishably fused 
into a continuous ridge. 
No caudal vertebrae of this genus have as yet been identified, though 
the character of the tail may be inferred from that of the sacrum. 
The ribs are much more slender than those of Nesodon , but otherwise 
so like them as to require no particular description. The sternum is still 
unknown, but was doubtless essentially similar to that of Nesodon. 
Appendicidar Skeleton. — The scapula (PI. XXVII, figs. 8, 9) closely 
resembles that of Nesodon , but differs in a number of details, as may be 
readily seen on comparing Figs. 1 and 2 of Plate XII. The outline of 
