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 like that of the lumbars 

 and inclines slightly forward. Transverse processes are absent from the last two thoracic 

 vertebra?, which display the feature, very unusual in an ungulate, of large and conspicuous 

 anapophyses. 



As far back as the eleventh 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 cavity which receives the wedge-like projec- 

 tion from the eleventh. 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 

 zygapophyses proper ; in section these processes have an S-like outline, and they constitute 

 a joint of great strength. 



The lumbar vertebrae (PI. XVIII, Fig. G), 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 mi 

 the first, second and sixth vertebra?, 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 



