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PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
canal is relatively larger and the spine lower and less massive, but more 
produced anteriorly. (5) The postzygapophyses are more oblique, pre- 
senting more ventrally, less laterally, and their long diameter is antero- 
posterior, not dorso-ventral. (6) The transverse processes project less 
laterally and more posteriorly. 
The succeeding cervical vertebrae are smaller and lighter propor- 
tionately than those of Nesodon and have narrower neural arches, leaving 
wider intervertebral spaces ; the neural spines are very low and but 
feebly developed, except on the seventh vertebra. The transverse pro- 
cesses are more slender than in Nesodon and have no such development 
of the inferior lamella as in that genus. 
The thoracic vertebrae (PI. XXVI, fig. 12) differ from those of the last 
named genus chiefly in the form of the neural spines. In the anterior por- 
tion of the region the spines are long, laterally compressed and thin and 
have a strong backward inclination, but they do not have any such exag- 
gerated length as in Nesodon and Toxodon and there is no hump at the 
shoulders. Posteriorly, the spines decrease in length very gradually and, 
owing to the upward curvature of the back-bone in this region, the tips of 
the spines lie in nearly the same horizontal plane throughout, which is in 
marked contrast to the arrangement seen in the larger genera (see PI. XII, 
figs. 1 and 2). Behind the middle of the thoracic region the spines are 
quite low and weak, becoming broader and stronger in the posterior region, 
where they lose their backward inclination and become nearly erect. 
Cylindrical, interlocking zygapophyses are present only on the last two 
vertebrae and metapophyses only on the last. In all of the thoracic verte- 
brae, except the first and last, the neural arch is perforated on each 
side by a conspicuous foramen for the passage of the spinal nerve. 
Of the lumbar vertebrae (PI. XXVI, fig. 1) probably five were present 
normally, though no individual has yet been found in which all of 
the lumbars are preserved. As compared with those of Nesodon , 
these vertebrae have relatively lower and broader neural spines, which are 
either erect, or have a slight backward inclination, none of them inclining 
forward, while the transverse processes are longer, narrower and more 
antroverted. On the penultimate lumbar the transverse processes are 
broader than on the preceding vertebrae and on the last one they become 
very much broader and have articular facets for those of the penultimate 
lumbar and first sacral, as already described for Nesodon. In all 
