280 THE OSTEOLOGY OF ELOTHERIUM. 
chamber, but toward the yentral side they rapidly contract, forming narrow strips 
between the squamosal and frontal. Throughout their length the parietals unite to form 
the very high, thin and plate-like sagittal crest, which is one of the most characteristic 
features of the skull. In the European species, #. magnum, this crest has a remarkably 
straight and horizontal course, but in the known American species it is gently arched 
from before backward. Large sinuses are developed in the parietals, so that the cerebral 
chamber is eyen smaller than it appears to be, when viewed from the outer side. These 
sinuses extend over the entire roof of the cerebral fossa, even invading the supraoccipital ; 
they appear to be traversed by numerous small trabeculee, the ends of which are seen, in 
the sagittal section, embedded in the matrix which fills the sinuses. 
The frontals are much larger than the parietals. In the postorbital region they are — 
very narrow, in conformity with the very small size of the brain, but at the orbits they 
expand widely to form the broad, lozenge-shaped forehead, which is convex from side to 
side, though slightly depressed, or “dished” in the middle; the supraciliary ridges are 
very inconspicuous. Anteriorly the frontals diverge to receive the nasals between them, 
sending forward long, pointed nasal processes, which, owing to the great elongation of the 
muzzle, are widely separated from the premaxillaries. The orbit is large and projects 
prominently outward ; it is completely encircled by bone, the long and massive postorbital 
process of the frontal uniting suturally with the shorter process of the jugal. The orbits 
do not rise above the leyel of the forehead, as they do in Hippopotamus, and present 
more anteriorly, less directly outward, than in that animal. Mention has already been 
made of a groove on the orbitosphenoid, which terminates below and behind in the fora- 
men lacerum anterius; this groove is continued upward and forward upon the frontal, 
steadily widening as it advances. The postero-superior ridge bounding the groove is the 
more prominent ; it extends almost to the postorbital process, from which it is separated 
by a distinct notch, while the antero-inferior ridge dies away within the orbit. In most 
of the American species the forehead rises yery gradually and gently behind to the sag- 
ittal crest, but in F. imgens the rise is much more sudden and steep. The frontal sinuses 
are large, giving the conyex shape to the forehead which has been described; these 
sinuses appear to communicate with those formed in the parietals. 
Except posteriorly, the sywamosal forms but little of the side-wall of the cranium, its 
suture with the parietal curving abruptly downward and forward; its compressed and 
prominent hinder margin forms nearly the whole of the lambdoidal crest, though a con- 
tinuation of it extends upward upon the supraoccipital, ending in the wing-like processes 
of that bone. The zygomatie process is enormously developed ; it extends widely out- 
ward from the side of the skull as a massive, vertical plate, which is shaped much as in 
Hippopotamus, and is not continued forward as a broad, horizontal shelf, such as is found 
