96 DINOCEIIATA. 



The Ulna. (Plate XXX; and woodcuts 110-111, below.) 



The iilna in the iJinocerata is a solid and heavy bone, longer than the 

 radius, as usual, by the length of the olecranon process. Except near the 

 distal end, it is larger and stouter than that bone, to which it was united in 

 life bv ligaments only, but in such a manner as to allow of little motion 

 between them. The shaft of the ulna always made, even at its utmost 

 extension, a distinct angle with that of the humerus. 



The idna in Dinoceras is proportionall}- less robust than in the 

 elejihant. Its distal end is comparatively smaller than in that animal, and, 

 at the ])roximal end, a much smaller jirojjortion of the articular surface for 

 the humerus is furnished by the ulna. 



The olecranon process is robust, as in the Proboscidians, but it is 

 carried farther above tlie articular surface, and less directly behind it, than 

 in that grouj). It is much higher within than without, and posteriorly, it is 

 strongly roughened as low down as the middle of the humeral articulation. 

 It is only moderately produced backward, and descends into a broad 

 ridge, insensibly blending below with the shaft of the bone. 



Below the humeral articular surface, the shaft of the ulna is 

 sub-triangular in section, or, near the distal end, some\\hat quadrilateral. 

 Along the posterior and outer side of the bone, is a rounded ridge, running 

 from the olecranon process above, to the outer angle of the articular face 

 below. 



The face by Mhich the nlna is applied to the radius is broadly 

 excavated, and strongh' roughened above, where it is nearly on the front 

 surface of the bone. It is moderately flattened along the shaft of the 

 bone, and is carried around to the inner surface toward the distal end, 

 where it is Ijroad, Hat, and distinctly roughened. 



The anterior face of the bone is also flattened near the distal end, 

 and separated from the outer face by a ridge, which extends upward to 

 near the middle of the shaft. The postero-external face of the bone is 

 flattened, or only moderately rounded, and is somewhat excavated behind 

 the lower part of the humeral articulation. 



