334 MEMOIRS OF THE CARNEGIE MUSEUM. 
The Humerus. 
(Plate LXVI.) 
The humerus, when compared with that of Titanotherium, is long and slender. 
The head is quite large and the articulating surface is evenly rounded. The 
tuberosities, though robust, are not more strongly developed than in other Oligo- 
cene and Miocene Perissodactyla, but project above the articular surface very 
much as in the latter. The bicipital groove, as stated by Peterson (I. c., p. 745), 
is single, quite broad, but shallow when compared with that of other Perisso- 
dactyla. The deltoid ridge is prominent, extends well down on the shaft, and is 
flexed backward over the external face of the shaft. The shaft below the deltoid 
ridge is trihedral in cross-section, due to the continuation on the anterior face 
of the shaft of a prominent ridge from the deltoid downward to the supratrochlear 
fossa (see Plate LX VI) as well as to the heavily developed posterior internal angle 
of the shaft, and the development of the ectocondylar ridge. 
The distal end of the humerus is quite unlike that of the Perissodactyla gener- 
ally, and recalls some of the features which occur in the Urside among the carni- 
vores. ‘This end of the bone has a primitive appearance, and has already been 
compared by Peterson with Phenacodus from the early Tertiary (l. c., p. 746). 
The distal extremity is much expanded transversely, the trochlea is very broad, 
with well-rounded articulating surfaces for the radius, and the intereondylar ridge 
is represented by a large, evenly convex area for the ulna, close to the deepest 
portion of the trochlea, an arrangement unlike the more or less decided ridge which 
is generally found at this point in the Perissodactyla. The ectocondylar ridge is 
prominent, but not so much so as in other persissodactyls, e. g., the Titanotheriide, 
while the strong development of the entepicondyle is entirely unlike what is found 
in the true Perissodactyla, and strikingly suggests what is seen in Ursus. The 
animal was evidently provided with an unusual development of the pronator teres 
and the different flexor ligaments of this region. The anconeal fossa is deep and 
broad, while the supratrochlear fossa is rather small and shallow. 
In Nestoritherium pentelici the proximal end of the humerus, as represented 
by a cast of the specimen preserved in Paris, is injured. The articulating surface 
of the head is, however, preserved, and is apparently identical in its general features 
with that of Moropus. The deltoid crest appears to decrease more gradually in 
its downward course, and the anterior face of the shaft presents a heavier and more 
rounded ridge running from the deltoid to the supratrochlear cavity than in the 
American genus. The ectepicondyle is more, and the entepicondyle less, developed 
