THE SKULE OF PALEORHINUS 143 
articulation. The external fenestra is quite elongate though its 
exact limits are unknown. The probable outlines are indicated in 
the figure. Only a portion of the posterior margin of the internal 
fenestra remains, together with the lower margin of the small internal 
mandibular foramen. None of the symphysis is present. 
Owing to the condition of the mandible but few sutures can be 
made out. However, that between the articular and the surangular 
on the broad, vertical posterior face of the jaw is clearly distinguish- 
able. The outlines of the posterior portion of the angular are also 
quite distinct. The articular forms the inner two-thirds of the 
articulation with the quadrate, while the outer third is formed by 
the surangular. The articular also forms nearly all of the transverse 
vertical area on the posterior extremity previously mentioned. At 
the inner border of this area is given off a strong, subrectangular 
process which is widely separated from the inner face of the jaw 
and extends nearly parallel with it. The main part of the articular 
extends forward for some distance, forming the lower margin of the 
internal fenestra. It may extend as far forward as the internal 
mandibular foramen, as stated by McGregor to be true in Phyto- 
saurus, but this cannot be determined. 
Angular.—This element is exposed for a width of about an inch 
on both sides of the ramus, whose lower margin it forms. It prob- 
ably forms the posterior angle of the jaw and constitutes its margin 
for a considerable distance under the fenestree. 
Surangular.—The surangular forms nearly all the outer face of 
the mandible in its posterior part and makes up the high crest of the 
jaw, besides entering into the articular surface which meets the 
quadrate. It is ornamented a little above the middle of its height 
by a strong, nearly horizontal ridge, slightly concave upward, which 
starts below the articulation, where it has a width of nearly one-half 
inch. It narrows anteriorly and becomes quite sharp before it 
disappears. 
The limits of the splenial on the inner surface and those of the 
dentary on the outer cannot be determined. Probably they corres- 
pond with those of Belodon and M ystriosuchus. 
The outer surface of the mandible is quite rugose in its hinder 
part and somewhat so farther forward. The rugosities consist 
