244. MEMOIRS OF THE CARNEGIE MUSEUM. 
The external face of the ascending ramus has not the rugose surface and 
everted sharp lower margin of the angle supporting the masseter muscle seen in 
Equus; on the other hand, the temporal fossa is deeper and fully as large. The 
coronoid process is of considerably greater antero-posterior diameter than in the 
horse, projecting backward to about the same extent, but terminates in a trihedral 
point. The sigmoid notch has nearly the same proportions as in Equus, while the 
region of the condyle is heavier. The articulating surface of the condyle itself is 
quite flat in order to conform to the glenoid cavity of the skull already described. 
Immediately below the condyle on the inner side is a deep groove for the protection 
of the blood-vessels. There is a tubercle on the lower border of this groove as in 
the horse, but more strongly developed than in the latter animal. The pterygoid 
fossa is deeply excavated and its rugose surface provides abundantly for the attach- 
ment of the muscles. The dental foramen is of large size, in order to provide 
sufficient nourishment for the heavy dentition of the inferior maxillary. 
The lower jaw of Nestoritherium reveals a strong general resemblance in its 
configuration and proportions to that of Moropus, but in Nestoritherium, and to a 
less extent also in Macrotherium there is a tendency to a thickening of the lower 
margin of the mandible. The outer and inner margins of the ramus in Moropus 
are evenly curved from above downward, whereas in the European genera 
there is externally a lateral ridge extending nearly the whole length of the 
ramus, and internally a corresponding shallow fossa, no trace of either of which 
is found in the numerous lower jaws of Moropus before us. The mandible in 
Macrotherium is proportionally shorter and more robust than in the American 
genus, the muzzle of which was undoubtedly longer and more pointed. In Circo- 
thervum the mandible is shorter still, without incisors, and the diastema between 
the premolars and the canine much shorter than the diastema between the pre- 
molars and the incisors in Moropus. 
MEASUREMENTS OF MANDIBLE. 
No. 1604 No. 1758 
(elatus), (petersont) j 
mm. nm. 
Total length of the lower jaw, incisors included........ 500 434 
Length of mandibular symphysis.......0+...--+-+--- 103 88 
Diameter from angle of jaw to and including P........ 385 334 
Diameter from angle of jaw to and including M;....... 185 159 
Depthvoteraniiishatidiashen aan sees tener en ene 30 28 
Depth: of ramustateRosar eee ee ee eee 60 58 
Depth: ofmamiuis jst Visi caer epee eee eet: 80 68 
Depth of ramus at coronoid process................5. 230 197 
Depthrof ramus/apicondyles. nicest leis crete 180 138 
