24 
MUSEUM BULLETIN NO. 12. 
The suture between the left epinasal bone and the left 
nasal is well shown in the figure of the skull of Triceratops elatus 
Marsh, forming Plate XLIII of Hatcher’s monograph. In T. 
elatus the form and position of the epinasal (Plate X, figure 1), 
as seen in side view, is very similar to that of Eoceratops (Plate 
X, figure 2), with this difference that in Eoceratops it is more 
under the upper anterior end of the nasal which extends over it. 
Apparently the epinasals are to be classed with the epi- 
postfrontal (supraorbital horn-core) the epi jugal, the epoccipitals 
(episquamosals and epiparietals) the rostral and the predentary 
as having a dermal or epidermal origin. But whereas the epi- 
parietals were subject to great enlargement (Styracosaurus) 
as were also the epipostfrontals, the epinasals always remained 
small taking a subsidiary part only in the formation of the 
nasal horn-core. Increase in size in the nasal horn-core was 
dependent on the nasals which extended over and were prolonged 
above the epinasals, the latter acting as basal supports and be- 
coming ankylosed to the nasals and to each other. 
In Plate X the nasal horn-core is shown in four species of 
horned dinosaurs {Triceratops elatus , Eoceratops canadensis , 
Brachyceratops montanensis , and B. dawsoni ) illustrating as many 
phases of nasal horn-core development from the incipient horn- 
core made up almost entirely of the epinasals, through pro- 
gressive stages of nasal enlargement until the horn-core consists 
mainly of the prolonged nasals with the complete subservience 
of the epinasals. In T. elatus the nasals are slightly elevated 
behind the epinasals, in E. canadensis they are sufficiently 
prolonged to cover the epinasals above, in B. montanensis 
(Plate X, figure 3) they are further enlarged by an upward 
extension, while in B. dawsoni (Plate X, figure 4) a full develop- 
ment of the horn-core is reached with their still further increase 
in size to form a weapon of imposing proportions. 
In Plate XI is figured one of two remarkably fine skulls 
of Centrosaurus apertus from the Belly River beds of the type 
locality. This skull in which the nasal horn-core is abnormally 
bent downward in its upper half, belongs to the collection of 
1914. In the other, discovered in 1913, the natural forward 
curve of this horn-core is preserved. 
