6 
MUSEUM BULLETIN NO. 12. 
The nasal meets its fellow in a flat, vertical, triangular 
surface of contact which extends, with increasing depth, from 
the prefrontal suture to nearly the full depth of the bone in 
front. This large sutural surface occupies more than one-half 
of the inner surface of the bone and must have given great 
strength to the anterior nasal region. Behind this extent of 
contact the inner surface of the bone is excavated and the bone 
is reduced in thickness. The anterior descending process dis- 
plays a well defined flat, oval surface on its inner front face 
for its sutural union with the upper limb of the premaxilla. The 
posterior descending extension is divided into two unequal 
parts by a deep groove at its lower end to receive the ascending 
posterior limb of the premaxilla. Anteriorly and facing obliquely 
outward and forward, there is a shallowly concave sutural surface 
of crescentic outline for the reception of a separate bone which, 
with its mate and the anterior end of the nasals, formed the nasal 
horn-core. This separate ossification is transversely compressed, 
higher than long, pointed above, thickest at the centre and thin 
toward the hinder and lower margin. Its outer surface is convex, 
flush behind with that of the nasal, and rounds forward and in- 
ward to the median line. Its inner surface shows that it met its 
fellow in a vertical surface in the median line. Its outline is 
convexly curved behind and below, and almost vertical in front. 
The nasal rises upward and extends over the ossification nearly 
as far forward as the front face of the latter which at its lower 
end is considerably in advance of the proximal end of the 
anterior descending nasal process. 
The nasal horn-core of Eoceratops is thus seen to be formed 
by the nasals with the assistance of two separate bones, which 
may be called the epinasals, anterior to the nasals, the median 
vertical plane of contact between the two pairs of bones dividing 
the horn-core into two equal parts. This vertical, longitudinal 
division of the nasal horn-core is seen in the type specimen of 
Brachyceratops dawsoni (Plate VI, figure 3), and has had special 
attention drawn to it by Gilmore in his description of B. montan- 
ensis . In the type specimens of E. canadensis and B. montanensis 
the vertical division of the horn-core is continuous due no doubt 
to juvenility; with greater age coossification would be expected. 
