756 MR. D. M. S. WATSON ON 
the parietal, but it is certain that the two bones met in a median 
suture which is only interrupted by the long cylindrical tunnel 
which forms the large pineal foramen. 
The posterior border of the bone is covered by the interparietal. 
Anteriorly it must meet the frontal, but the suture is never 
visible. The lateral border is completely covered by the post- 
orbital. 
The excessive thickness of the bones makes them come into 
contact with the upper border and anterior face of the supra- 
occipital. 
The postorbital (P.O.) is a large and very remarkable bone. 
It forms the massive bar behind the orbit, and has a very long 
suture with the squamosal in the zygomatic arch below the 
temporal fossa. 
Above the orbit in R. 3594 it meets the small post-frontal, but 
in that specimen on its lower surface (on the right side) it can 
be distinctly seen to join the prefrontal in a long suture running 
inwards nearly to the middle line. The extremely thick and 
massive bone then meets the parietal and covers the whole of its 
outer surface, sending out a process in contact with the front face 
of the interparietal and tabulare to be finally covered by the tip 
of the parietal ramus of the squamosal, so that the temporal fossa 
is entirely bounded by these two bones. 
The sutures between the postorbital, frontal, and prefrontal 
are not visible on the outside of the skull. 
The postfrontal (Pr.FR.) is a very small bone forming a small 
part of the orbital margin and entirely surrounded by the 
prefrontal and postorbital (R. 3594). 
The prefrontal (Pr.FR.) is a very massive bone forming the 
front upper quadrant of the orbital margin. On its ventral 
surface it has a long suture with the postorbital and likewise 
joins the postfrontal, frontal, nasal, and lachrymal. 
The lachrymal (Lac.) (R. 3594) is a small bone forming the 
front of the orbit and articulating with the prefrontal, nasal, 
maxilla, and jugal. There is no lachrymal foramen. 
The nasal (Na.) (R. 3594) is a large bone which plays a great 
part in the structure of the face. The two bones are in contact 
in the middle line posteriorly, where they are very thick, but their 
thinner anterior portions are separated by the very long internarial 
processes of the premaxille. The outer border of the nasal has a 
suture with the prefrontal, lachrymal, maxilla, and septomaxilla, 
and is entirely excluded from the nostril by the latter bone. 
The visceral surface of each nasal has a sharp ridge, the two 
together forming a groove for the olfactory nerves. 
The premaxilla (P.Mx.) of R. 3594 is a very remarkable bone. 
It has a suture with its fellow, with which it forms the rounded 
extremity of the snout. Its tooth-bearing margin is short and 
wide, and its inner edge forms part of the anterior border of the 
posterior naris. Medial to this opening it sends back a process 
along the upper surface of the prevomer. The dorsal surface of 
