29 
SKULL 
When viewed from above the skull (Plate XVII, figure 1) resembles 
that of Euoplocephalus tutus as figured by Gilmore 1 and, as in that genus, 
is broader than long, has a broad muzzle, and a slightly overhanging 
occipital crest. Posteriorly it is nearly flat, but the anterior half is 
slightly arched longitudinally and transversely. The whole surface is 
covered wfith thick, moderate-sized scutes which are thoroughly co-ossified 
with each other and the skull and surrounded by rather deep 
circumscribing grooves. Unlike Euoplocephalus there is no large central 
plate covering the nose, but just behind the raised rugose plates w T hich 
form the superior border of the external nares is a pair of moderate-sized 
plates which meet on the midline. Behind these is a single plate on the 
midline, but it is not conspicuously larger than the others. All of the plates 
on the anterior portion of the skull have a flat or concave superior surface. 
Above the orbit and continuing back to the supero-posterior angle of the 
skull is a series of sub-triangular plates with the apexes directed upward. 
These give the side of the skull, from the orbit backward, an almost vertical 
aspect. On the postero-tnferior angle of the skull is a large sub-triangular 
plate with the apex pointing outward and downward. The apexes of these 
scutes form the widest part of the skull. These resemble the homologous 
plates of Euoplocephalus 2 and Ankylosaurus 3 and extend well below the 
distal ends of the quadrates. 
When viewed from the side (Plate XVII, figure 2) the head is more 
depressed than in any other plated dinosaur known to the writer. Its 
greatest height, including the mandible, is only slightly more than one-third 
of the length. 
The limits of the bones of the top and sides of the skull are, in most 
cases, not discernible because of the covering of dermal plates. 
The external nares are long, narrow, transverse slits, placed on either 
side of the midline of the broad muzzle and separated by the premaxillse. 
They face almost directly forward and are surrounded by a high ridge 
of dermal bone. The greatest vertical diameter is 20 mm. and the 
transverse diameter is 75 mm. 
The orbit is moderately far back, broadly lenticular in outline, and 
faces outward. It is surrounded by thin dermal plates which at the anterior 
extremity stand out from the inferior border of the rim, thus giving certain 
protection to the eye from the front. 
The lateral temporal fossa is completely hid from the external view 
by a covering of small, thick, irregular-shaped dermal scutes. This mass 
of thoroughly fused ossicles completely fills the space behind the orbit, 
between the sub-triangular plates on the supero-external angle of the 
skull and the large plate on the postero-inferior angle. 
The supratemporal fossoe are also completely covered by the derma 1 
scutes. 
The foramen magnum is small, subcircular in outline, and is overhung 
by the short occipital crest. 
* Gilmore, C. W.: The Canadian Field-Naturalist, vol. XXXVII, No. 3, PI. 11 (1923). 
8 Loc. cit. 
* Ankylosaurus magniventris Brown, Dinosaurs by W. D. Matthew, A. M. A. H. Handbook No, 5, Fig, 35. 
