82 O. C. Marsh on the Affinities of the Brontotheride. 
Among the more marked characters of the Brontotheride, 
which readily distinguish them from the Rhinocerotide, appar- 
ently their near allies, may be mentioned the following :—T here 
are four short and thick toes in the manus, and three in the pes. 
The skull supports a pair of large horn-cores, placed trans- 
versely, as in modern Artiodactyls.* There are well developed 
canine teeth in both jaws. The molar teeth, above and below, 
are not of the Rhinoceros type, but resemble those of Chalico- 
erium. 
of that author, differed essentially in having four lower pre- 
molars, and in the absence of a third trochanter on the femur. 
Less important differences are seen in the composition of the 
teeth, and in the diastema between the upper canine and first 
premolar. 
The skull in Brontotherium is elongated, and resembles in its 
general features that of Fhinoceros, The occipital region is 
greatly extended vertically, and deeply concave posteriorly. 
The brain cavity is unusually contracted. The vertex is con- 
cave longitudinally, and convex transversely (Plates 1 and Ii). 
he zygomatic arches are massive, and much expanded. 
orbit is small, and continuous with the elongated temporal fossa. 
e nasals are greatly developed, and firmly codssified. They 
support entirely, or nearly so, the large divergent horn-cores. 
Their anterior extremities are produced, and overhang the large 
narial orifice. The premaxillaries are diminutive, and do not 
extend forward so far as the end of the nasals. The palate 1s 
deeply arched above, especially between the premolars. The 
posterior nares extend forward nearly to the front of the last 
molar. e lachrymal forms the anterior margin of the orbit. 
The malar extends forward beyond the lower margin of the 
orbit. The infra-orbital foramen is large, and situated well for- 
war e zygomatic process of the squamosal is elevated, and 
incurved above. There is a large post-glenoid process, and a 
massive, and somewhat shorter paroccipital process (Plate 1). 
The posttympanic process of the squamosal is large, and quite 
external to the paroccipital process. The occipital condyles 
are large, and well separated. 
* Rhinoceros pleuroceros Duv., from the Miocene of France, has 
the nasals, not unlike those in Dinoceras 
processes. 
of small horn-cores on . R. minutus Cuv 
has somewhat similar 
