336 MEMOIRS OF THE CARNEGIE MUSEUM. 
rugosity on the lower half of the radial face of the shaft for muscular attachments. 
From this point downward to the distal end the dorso-radial angle of the shaft is 
developed into a strong ridge, which terminates in the greatly produced styloid 
process of the radius somewhat as in Titanotherium. Dorsally there is a broad, 
deep, well-defined groove for the extensor tendons. Peterson (I. c., p. 746) says: 
“The distal end of the radius and ulna together have a transversely broad aspect, 
the carpal articulation is characteristically plain without the prominent border 
ridge] which separates the scaphoid and lunar facets in other Perissodactyla.”’ 
The articular surface for the cuneiform on the ulna projects only very slightly 
below the radius, and forms with the lunar articulation on the radius a continuous 
and gently curved surface. The suture between the radius and ulna is well indi- 
cated on the distal articulating surface of the bone. 
The Ulna (Pl. LX VIT).—The ulna is rather heavy, its olecranon process heavy 
and truncated, convex and very rugose externally, concave and smooth internally, 
and without a tendinal groove supero-an- 
teriorly. The sigmoid notch is quite deep; 
the principal part of its lower portion located 
on the radial side and facing upward and 
forward, while on the ulnar side the coronoid 
process is rather small. Below the sigmoid 
cavity there is on the anterior face of the 
shaft a broad attachment for the correspond- 
ing surface on the head of the radius. The 
shaft is quite heavy, trihedral in cross-sec- 
tion and twisted to conform to the curva- 
ture of the shaft of the radius. 
The radius and ulna in Nestoritheriwm 
pentelici closely resemble the same bones 
Fie. 78. 1. Distal articulating surface of jn Moropus. In the remains from Greece 
left ulna-radius of M. petersoni. X%. 2, do. 
the olecranon process is, however, more trun- 
cated; the upper part of the sigmoid notch 
less prominently developed; and the shaft 
proportionally heavier. In fact the forearm as well as the humerus are shorter 
and stouter in Nestoritherium than in Moropus. 
of right ulna-radius of Nestoritheritwm pentelict. 
xt. 
If the radius of Macrotherium figured by Blainville belongs to the same indi- 
vidual as the humerus depicted by him, the lower arm in this genus must have 
been proportionally much longer than in either Moropus or Nestorithervum. 
