HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 243 
borders of the lower jaw form a more nearly perfect right angle in Moropus. Back 
of the incisors the long and rather delicate ramus of the lower jaw is much 
constricted laterally as in the horse. The mental foramen is also sometimes 
D. 
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Fic. 16. Mandible of M. petersoni (?) (No. ee 1, external view; 2, superior view. #4. 
located immediately back of the greatest constriction, as in Equus. The position 
of this foramen is, however, variable in Moropus, and there are generally two and 
sometimes three foramina distributed on the external and lower faces of the con- 
stricted area of the ramus. The alveolar border is suddenly raised above the 
diastema, in this respect differing from the horse in which the border of the dia- 
stema rises more gradually. Along the external margin of the alveolar border of 
the lower jaws of specimen No. 1604 there is a prominent ridge, which is generally 
less developed in younger individuals. The internal face of the horizontal ramus 
is slightly more convex than in the horse and more nearly like that of the tapir. 
As in the horse, there is a liberal space on the alveolar border between M; and the 
base of the coronoid process, but Moropus differs in having this portion of the 
ascending ramus much heavier, and also in having a much larger, more rugose, 
and deeper anterior fissure for muscular attachments; in consequence the external 
and internal margins at the base of the coronoid process are much heavier than 
in the recent horse, and the external margin flares outwardly as it does not in the 
horse. 
