PETERSON: THE AMERICAN DICERATHERES. 



443 



Fore Limb. 

 Scapula. The scapula is long, narrow, and recurved. It is perhaps some- 

 what narrower than in earlier types (C. tridadylus, Osb.) and nearer the propor- 

 tions found in more recent forms (R. pachygnathus or R. bicornis Wagn.) In 

 general the outlines are very similar to those of these species. The coracoid is 

 prominent, the supra-scapular notch quite deep. The spine, which nearly equally 

 divides the supra- and infra-spinous fosss, terminates in a very heavy and retro- 

 verted process. There is a third fossa at the coracoid border immediately above 

 the suprascapular notch, which is separated from the supraspinous fossa by a 



Fig. 30. Diccraiherium cooki Peterson. Xo. 2473, Coll. Carnegie Museum. External views of scapula. 



X i. 



somewhat prominent vertical ridge. The fossa itself, however, is rather shallow 

 and of relatively small size. (See Fig. 30). There is very iittle variation in the 

 details of the scapula in fully adult animals, robustness and size excepted. 



Humerus. The humerus is short and heavy. The tuberosities of the proximal 

 end, though not as heavy in proportion as in some of the recent Rhinoceroses 

 {R. bicornis), are nevertheless, very prominent and the bicipital groove has a 

 tendency to become double, i.e., separated by a broad, but very low ridge, approach- 

 ing the condition in the recent Rhinoceros where the bicipital tubercle is more 

 prominent. Distally the bone has furthermore a great transverse diameter due to 



