8 
Cranium. The cranium proper or brain-case of Edmontosaurus 
though small in proportion to the size of the head was strongly put together. 
The bones entering into its formation were thick and between many of 
them coossification took place; at least in the paratype, on which the present 
description is principally based, the brain-case, although excellently 
preserved with wonderful detail of structure and form, exhibits few of 
the sutures externally in the side walls and basicranial axis. In the brain- 
cavity none of the sutures have been detected. 
In Edmontosaurus, and apparently in the Hadrosauridae generally, 
ossification took place throughout the cranium, in fact the brain-case in 
the Hadrosauridae appears to have been as complete as in the Ceratopsidae, 
and in both groups an early closing of the sutures marked a departure 
from conditions in the typical reptilian skull in which the cranial elements 
tend to remain distinct throughout life. 
In the paratype of Edmontosaurus, in the external surface of the 
sidewalls of the cranium, the suture between the alisphenoid and the 
prootic is preserved above the foramen ovale. In a large surface extending 
forward from the alisphenoid, representing the orbitosphenoid and the 
presphenoid no sutures are seen marking the separation of these bones 
from each other, although their upper boundaries are very distinctly and 
clearly defined, and in the case of the orbitosphenoid and the presphenoid 
their lower limits also. 
Interiorly the suture between the basi-occipital and the basisphenoid 
is visible on either side, but not near the midline, and it can be traced 
upward on the side walls for a short distance before trace of it is lost. 
Also in the occipital condyle the division between the basi-occipital and 
the exoccipital is clear and distinct not only beneath but externally and 
posteriorly as well. 
An early and perfect union of the opisthotic with the exoccipital, and 
of the epiotic with the supraoccipital would be expected, but in the side 
walls behind the foramen ovale no sutures can be detected suggesting a 
division between any of the periotic bones. Nor is there a suggestion of 
the extent of the supraoccipital bone. 
The cranial foramina are well preserved and, relying on them, with, 
the aid of the few sutures that are visible, the proportionate size and relation 
to each other of the elements entering into the formation of the brain-case 
are fairly well established. 
Measurements of Skull of Type of Edmontosaurus. 
Mm. 
Length of skull measured in a straight line from the posterior edge of the exoccipital 
process(paroccipital) to the centre of the anterior premaxillary margin 1114 
Horizontal length from anterior premaxillary margin to a point vertically below 
the preoccipital edge 1066 
Height from level of posterior end of nasal at the midline of skull to lower surface 
of dentary ; • • •. 
Height of orbit measured vertically down from centre of frontal contribution to 
orbital rim 205 
Width of orbit at mid height 180 
Length of supratemporal fossa 153 
Maximum width of same near its anterior end 85 
Width of infratemporal fossa toward its lower end 60 
Length of quadrate 420 
Breadth (antero-posterior) of external face of same at midheight 76 
