238 MEMOIRS OF THE CARNEGIE MUSEUM. 
The lower surface of the basisphenoid is rounded and clasped anteriorly on 
either side by the thin posterior plates of the vomer, which unite in the middle of 
the median fossa to form a thin knife-like crest. There is no suture visible between 
the basisphenoid and the presphenoid in the material before the writer, the two 
bones appearing to be, where exposed to view, thoroughly codssified. The pre- 
sphenoid is almost completely covered by the posterior prolongation of the vomer 
much as in the rhinoceros, but with this difference that the downward projecting 
ridge formed by the posterior part of the vomer where it envelops the presphenoid 
is sharp and not rounded as in the rhinoceros, in this respect resembling the con- 
ditions which are also found in the tapir. The pterygoid processes of the basi- 
sphenoid are well developed on either side of the posterior margin of the posterior 
nares, codssifying behind with the basal portion of the alisphenoid. The 
sphenoidal fissure is well developed and even more so than in the horse, the rhi- 
noceros, or the tapir. The foramen lacerum medium is bounded externally by a 
thin bony plate which is an anterior projection from the front wall of the auditory 
bulla, and which passes anteriorly into the posterior margin of the pterygoid 
processes. This feature of the skull recalls what is found in the skull of the bison. 
The anterior limits of the palatine bones, like those in other Perissodactyla, 
lie opposite the anterior portion of M’, but the backward extension of the palatines 
is very unusual, the anterior border of the posterior nares being much further back 
of the cheek-teeth than in any recent forms, suggesting conditions found in some of 
the Uinta Titanotheres, e. g., Dolichorhinus fluminalis Riggs. Moropus differs in 
this respect from Macrotheriwm, where the anterior margin of the posterior nares 
(la votite palatine) on the median line is even with the anterior internal cusp of the 
last molar (cf. Filhol, ‘“‘Mammiféres Fossiles de Sansan,” p. 295). In Nestorz- 
thervum this margin lies opposite the transverse valley of M*, and therefore in a 
position intermediate between those found in Macrotherium and Moropus (Fig. 15). 
In Phenacodus from the American Wasatch the posterior narial opening is further 
forward than in the present form, while in some extinct Artiodactyla (Achenodon, 
Promerycocherus, Pronomotherium, ete.), the posterior nares are well back of the 
cheek-teeth, but in none of them as far back as in Moropus. The two palatines 
present posteriorly a U-shaped outline, the lateral sutures are very close to the 
alveolar border of the maxillaries, thence running backward, forming heavy proc- 
esses for the contact of the pterygoids. There are numerous small foramina 
distributed over the surfaces of the palatine plates. 
The parietal bones are long, and have a relatively smaller vertical diameter 
than in the recent rhinoceros or the horse, uniting anteriorly with the frontals 
