Peterson : Skeleton of Diceratherium Cookt Peterson. 277 



Niiu' caudals ha\c been acUlcd to tlie vnd of this series, twenty-six 

 in all. wiiich is approximately the correct number of vertebra* in the 

 tail. 



The ribs are ratlier long which gi\es the animal a large thoracic 

 ca\it\- simil.ir to t hat in .1. tridactylum. In their shape they are also 

 (piite similar to those of the latter species. The manubrium is an 

 elongated, laterally compressed, and vertically deep plate of bone. 

 Anlt'rior to the contact for the first pair of ribs there is a long heavy 

 process, extending directh' forward, constituting the greater half of the 

 antero-posterior diameter of the presternum. Posteriorly the bone is 

 slightly expanded transversely and has a rough surface for the attach- 

 ment of the succeeding segment of the mesosternum. The first two seg- 

 ments of the mesosternum are of considerably greater vertical diameter 

 than the transverse; the posterior end of the fourth sternebra is nearly 

 cubical in outline, while the fifth is broader than deep. The lumbar 

 region is rather short, the sacrum has four to five coossified centra, and 

 the caudal region is of moderate length. 



T.IMBS. 



The scapula is rather long and narrow; the spine is heavy and greatly 

 overhangs the postscapular fossa; the coracoid is prominent; the glen- 

 oid border is much concave supero-inferiorly, while the coracoid 

 border, some distance above the glenoid cavity, is greatly convex in 

 the same direction. The humerus may be regarded as short and 

 heavy, with a powerfully developed deltoid crest, a prominent supi- 

 nator ridge, a deep anconeal fossa, and the intercondylar ridge shifted 

 well towards the ulnar border of the trochlea. Proximally and dis- 

 tally the radius and ulna are well interlocked by rough attachments, 

 and in adult or old individuals the shafts come in contact with one 

 another by prominent and rugose ridges, which supported a heavy 

 cartilaginous band. The olecranon process of the ulna is large and 

 truncated and the shaft is comparatively heavy. 



The manus is functionally tridactyl. The fifth metacarpal is, 

 however, present in a rudimentary condition, while that of Acera- 

 therium tridactylum is said to be strictly tridactyl. 



The presence of mc. V in D. cooki led to a closer study of Professor 

 Osborn's memoir on "The Extinct Rhinoceroses" previously cited. 

 The illustration of .1. tridactylum on page 84 of this work appears to 



