296 THE OSTEOLOGY OF ELOTHEEITJM. 



Measurements. 



Fifth thoracic, height of neural spine. 291 



First lumbar, length 050 



Sixth lumbar, length 048 



Sixth lumbar, breadth across transverse processes 176 



Sacrum, length 098 



First sacral, width of centium 068 



Second sacral, width of centrum 025 



Anterior caudal, length 032 



Median caudal, length 063 



V. The Ribs axd Sternum. 



The ribs of Elotherium are decidedly smaller and lighter and indicate a less capacious 

 thorax than we should expect to find in such a large animal, a fact "which adds to the 

 apparent height of the skeleton, because of the long interval between the thorax and the 

 ground. 



The first rib is short, subcylindrical proximally, but broadening considerably at the 

 distal end ; it has only a slight lateral curvature, appearing nearly straight when viewed 

 from the front, but it arches moderately backward. The head is large and compressed, 

 and is separated by a deep and narrow notch from the very large and conspicuous 

 tubercle, which is also compressed laterally. The ribs increase gradually in length up to 

 the seventh or eighth of the series, and the posterior five, though successively shortening, 

 retain a considerable relative length throughout. The first five or six ribs are laterally 

 compressed and of moderate breadth, but the posterior part of the thorax is composed of 

 very slender and subcylindrical ribs, very different from those which we find in most 

 ungulates, except in the more primitive groups. The tubercle reaches its maximum of 

 size and prominence on the third rib, behind which it gradually diminishes in size and 

 becomes more and more widely separated from the head, and more sessile in position. 

 On the twelfth and thirteenth pairs the tubercles are absent, corresponding to the lack of 

 transverse processes on the twelfth and thirteenth thoracic vertebrae. 



In Hippopotamus the ribs are relatively very much longer, broader and heavier than 

 1 1 mse of Elotherium, and grow broader toward the hinder end of the thorax, where the 

 great bony slabs are in the sharpest possible contrast to the slender and subcylindrical 

 rods of tin- extinct genus. In Sus the ribs are more like those of Elotherium, but they 

 have not such a regular and symmetrical curvature a- in the latter. 



The sternum of Elotherium is a very remarkable structure, and although it is of 

 distinctly suilline type, it is, nevertheless, not altogether like the sternum of any known 

 genus, recent or fossil. The presternum, or manubrium, forms a very large, thin, com- 

 pressed and keel-shaped plate, which is especially remarkable for its great vertical depth, 



