HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 241 
The maxillary is of large size and in general outline closely suggests the same 
bone in the genus Hquus. As in the latter the ascending process furnishes the 
ereater portion of the side of the muzzle and is joined superiorly by the lachrymal 
and the nasal, as stated above. The infra-orbital foramen is of considerable size, 
larger than in Hquus, though not as large as in Rhinoceros and Tapirus, and is 
located over the anterior portion of M?. ‘The size of this foramen indicates a more 
liberal exit for and perhaps a greater supply of blood to the upper labial muscles 
than in the horse. The upper portion of the narial border is rather thin; it does 
not indicate any sutural contact with the premaxillary, and the border as a whole 
indicates a more gradual slope than it does in a younger specimen previously de- 
seribed.4* The anterior ends of both maxillaries are broken off; the right a short 
distance in advance of the cheek-teeth. There is a diastema of considerable 
length between the cheek-teeth and the maxillo-premaxillary suture, judging 
from the correspondingly long diastema of the lower jaw. ‘The alveolar border is 
quite long and is occupied by a set of powerful teeth. Back of M? there is an 
unusually long and heavy extension of the alveolar border quite unusual in the 
Perissodactyla. These processes of the maxillaries which project backward, furnish 
much lateral contact for the palatine plates, the extraordinary posterior develop- 
ment of which has already been pointed out. Externally the maxillary presents 
an even and gently convex surface over the cheek-teeth both supero-inferiorly 
and in the antero-posterior direction, there being, as stated above, no perceptible 
masseter crest as in the horse. The palatine plates have the same degree of trans- 
verse concavity as in the horse, and in the present genus they furnish approximately 
one-half of the palate between the cheek-teeth. Beyond the molar-premolar series 
the maxillaries are wanting in our specimen. 
The premaxillary of Moropus, as stated by Peterson (1. c., p. 740), is not known. 
However, judging from the long slender symphysis of the lower jaw, these bones 
were undoubtedly of considerable extent. They may have been edentulous, 
though, as pointed out by Peterson, the “lower jaws of adult specimens with 
incisors in place always show wear on the median pair, while the lateral teeth are 
almost entirely unworn” (i. c., p. 740, foot-note). When making the restoration 
represented on Plate LIII two small median incisors were inserted by the senior 
author, who modelled the skull. They may or may not have existed in nature, 
but the constant wear at right angles to the axis of the procumbent lower incisors 
seems to suggest that they must have met with some opposition, which it seems 
most reasonable to suppose to have been that of teeth located in the upper jaw. 
The genus Macrotherium had a relatively shorter skull. In this genus, 
18 Peterson, O. A., Amer. Naturalist, Vol. XLI, p. 740. 
