242 MEMOIRS OF THE CARNEGIE MUSEUM 
The Orbital Cavities (Figs. 1, 3, 5, and 7-10 and Plates XXVIII. and XXVI.).— 
The orbital cavity is irregularly oval in form, with the longer axis lying in the 
direction of the longer axis of the skull. It is bounded above on its outer margin 
by the prefrontals, the frontals and the postfrontals ; behind and below by the post- 
orbitals, and below in front by the jugal. Its upper anterior margin is bounded by 
the supraorbital. The inner walls of the opening are formed by the nasals, the 
frontals, the orbitosphenoids and alisphenoids, and the process of the postorbital, 
which is thrust in between the frontal and the alisphenoid. The anterior portion 
of the wall is in part formed by the thin plate of the lachrymal, which articulates 
along the inner margin of the supratemporal. 
The Narial Opening (Fig. 3).— The narial opening has been very accurately and 
correctly described and figured by Professor Marsh. It is, as he says, ‘“ very large, 
subcordate in outline, and is partially divided in front by the slender posterior proc- 
esses of the premaxillaries. It is situated at the apex of the skull, between the 
orbits and very near the cavity for the olfactory lobes of the brain.” 
The Preorbital Vacuities (Fig. 3 and Plates XXIII., XXIV., and XXVI.).— The 
preorbital vacuity is phenomenally large, but by no means as large as it is repre- 
sented in the restoration of the skull made by Mr. Hermann (A. M. N. H., No. 
969) (see Plate XX VI.) and its outline is quite different, so far as can be deter- 
mined from the specimens which are preserved in the United States National Mu- 
seum. A comparison of the type skull, a photograph of which is given upon Plate 
XXIII. and of the accurate drawing published by Professor Marsh with the photo- 
graph of the skull restored by Mr. Hermann (a photograph of which is given upon 
Plate XX VI.) will show the great difference which exists. Unfortunately this por- 
tion of the skull employed by Mr. Hermann in making his restoration was missing, 
and the margins of this opening are wanting in the specimen, and in the restoration 
are wholly artificial. 
The Mesial Foramen of the Maxillary (Fig. 8 and Plates XXITI., and XXIV.). — 
This opening, which does not occur, so far as is known, in any other genus of the 
Dinosauria, is about 5.5 cm.in length and about 3 em. in width on its longest diam- 
eters. It is situated half way between the outer and inner margin of the maxillary 
bone and about midway between the posterior margin and the anterior extremity of 
the bone. Itis very prominently and distinctly developed in both of the skulls, which 
are preserved in the collection of the United States National Museum. It has been, 
unfortunately, altogether ignored by Mr. Hermann in his restoration, and, as will 
be seen by reference to the photograph of this skull on Plate XXVI., it is not shown 
there. This foramen, which communicates with the interior of the nasal cavity, 
