THE OSTEOLOGY OF ELOTHERIUM. 293 
A change in the character of the facets for the rib tubercles occurs simultaneously 
with the shortening of the neural spines ; they suddenly become much reduced in size 
and are plane instead of concave. The transverse processes, however, remain very large 
and prominent as far back as the eleventh thoracic. In no case are these processes per- 
forated by vertical canals, such as occur in Sus. The twelfth thoracic is the anticlinal 
vertebra and has a nearly erect spine of lumbar type, though somewhat more slender 
than in the true lumbars. On the thirteenth the spine is quite lke that of the lumbars 
and inclines slightly forward. Transverse processes are absent from the last two thoracic 
yertebree, which display the feature, very unusual in an ungulate, of large and conspicuous 
anapophyses. 
As far back as the eleyenth vertebra the zygapophyses are of the ordinary thoracic 
type; they are small, oval facets, the anterior pair on the front of the neural arch and 
presenting upward, the posterior pair on the hinder part of the arch and presenting 
downward. On the eleventh thoracic a change takes place ; the anterior zygapophyses 
are as before, but the posterior processes are flat and present obliquely outward, rather 
than downward, the two together forming a prominent, wedge-shaped mass. The 
prezygapophyses of the twelfth vertebra are correspondingly modified; they present 
obliquely inward and together constitute a cayity which receives the wedge-like projec- 
tion from the eleyenth. Prominent metapophyses also make. their appearance on the 
twelfth thoracic. The posterior zygapophyses of the latter and both pairs of the thirteenth 
are of the cylindrical, interlocking type characteristic of the lumbars. These processes 
are remarkably complex and in a fashion that does not occur in Hippopotamus, but is 
found in Sus and many of the Pecora. The complexity is occasioned by the development 
of large episphenial processes, which give an additional articular surface above the 
zy gapophyses proper ; in section these processes have an S-like outline, and they constitute 
a joint of great strength. 
The lumbar vertebra (Pl. XVIII, Fig. 6), almost certainly six in number, have 
rather short, but massive centra. In the anterior part of the region the centra are some- 
what cylindrical in shape, but they become more and more depressed and flattened as we 
approach the sacrum. The neural canal is broad and very low, especially in the pos- 
terior part of the region. The neural spines are inclined forward and are of moderate 
height ; they are broad antero-posteriorly, but thin and laterally compressed, except at 
the tips, where they are thickened. The spine of the last lumbar is a little different 
from the others in being more erect and slender. Episphenial processes are present on 
the first, second and sixth vertebre, but not on the third, fourth or fifth. These 
processes are apt to be somewhat asymmetrical and better developed on one side than on 
the other, and it is probable that more extensive material would show them to be subject 
