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STRUCTURE AND AFFINITIES OF THE BRONTOTHERIDZ. 83 
size. The metacarpal bones are shorter than those of the Rhi- 
noceros, the first phalanges longer, and the second series shorter. 
The ungual phalanges are short and tubercular, as in the elephant. 
The femur has a small third trochanter, and its head a deep pit 
for the round ligament. At the distal end, the anterior articular 
surface is narrow, and the two edges are of nearly equal promi- 
nence, as in the tapir. There is a small fossa on the posterior 
side above the outer condyle. .The tibia is stout, and has a dis- 
tinct spine. The fibula is entire, but quite slender. The astrag- 
alus is shorter than in the , rhinoceros, and the superior groove 
more oblique. The cuboid face is larger than in Rhinoceros. The’ 
navicular has its distal facets subequal. There were three toes of 
nearly equal size in the pes, the first and fifth being entirely 
wanting. 
The ug known species of this group is Brontotherium ingens 
Marsh, which is represented in the Yale College Museum by a 
skull, nearly perfect, and other characteristic remains. The speci- 
mens preserved indicate that the animals to which they pertained 
nearly or quite equalled the elephant in bulk, and far exceeded in 
size any known Perissodactyls living or fossil. 
The skull in the type specimen of the species is well Tene 
in the accompanying plates, and its general characters have already 
been given. It is three feet in length, and twenty-two inches 
across the zygomatic arches. The most striking peculiarity of this 
cranium is the pair of huge horn-cores on the nasals. They are 
about eight inches in length, and extend upward and outward. 
They are triangular at the base, with the broadest face external. 
The two inner faces of each core are separated by a ridge, which 
is continued to the median line. The upper part of the horn-cores 
is rugose, and the base contains large air cavities. The free ex- 
tremities of the nasals are codssified, and nfuch elongated. They 
are rounded in front, slightly decurved, and the surface at the end 
is rugose. The orbit is of moderate size, and looks forward, out- 
ward and upward. The lachrymal foramen is small, and ovate in 
outline. The infra-orbital foramen is unusually large. There is 
no post-orbital process. The zygomatic arches are massive, and 
the squamosal portion widely expanded. The temporal fossa ex- 
tends far backward, and has over its posterior portion an obtuse 
Tidge. The occipital condyles are Eon S wide: apart, and 
extend slightly oe the —— eh The paroc- 
EE eann 
