53 
back, but slightly lower in elevation than the cerebrum, to the cerebellum 
beyond which it has a rapid descent to the foramen magnum. The inferior 
outline ascends gradually from the floor of the foramen magnum to the 
forwardly placed pituitary body which depends in line with the posterior 
part of the cerebrum. The lower outline of the olfactory lobes is horizontal 
in advance of the backwardly ascending lower surface of the cerebrum. 
Viewdng the cast from above or below the greatest breadth is across 
the cerebrum in great contrast to the comparatively slender olfactory 
lobes, and the less slender but narrow portion extending back from the 
cerebrum. 
The brain of Edmontosaurus, relying on the proportions of the cast 
of the brain-cavity, was about two and a half times as long as its maximum 
height, i.e., from the lower end of the pituitary body to the level of the 
upper surface of the cerebrum (cerebral hemispheres). For a little over 
half its length forward from the foramen magnum it is narrow, angulated 
above, and constricted on the sides over a considerable area above the 
auditory nerve. Forward it broadens greatly into the cerebrum and 
ends narrowly in the olfactory lobes. The cerebellum rising with a steep 
posterior slope, is laterally compressed, but does not reach as great an 
elevation as the cerebrum which is the highest part of the brain. The 
angulation of the upper surface continues forw^ard from the cerebellum 
and ends at a constriction deflning the hinder limit of the cerebrum. A 
lateral angulation runs obliquely downw^ard and forward from the cere- 
bellum to above the trigeminal nerve apparently marking the posterior 
boundary of the optic lobe. The constriction just mentioned (posterior 
commissure) is continued down the sides in advance of the optic lobe 
between it and the cerebrum (or behind the primary fore-brain or thalamen- 
cephalon if it were recognizable). 
The cerebrum is almost hemispherical in shape, broadly rounded in 
all directions above, and flatly convex transversely in its anterior surface 
which descends very rapidly to the olfactory lobes. Laterally where it 
reaches its greatest breadth it overhangs its flattened lower surface. The 
infundibulum extends downw^ard in line with the posterior part of the 
cerebrum (from the primary fore-brain) narrowing below wdth a backward 
inclination and terminating in the pituitary body. 
The olfactory lobes, not distinguishable as a pair in the cast, are 
produced horizontally forward and are together much broader than deep; 
they are transversely somewhat concave above and moderately convex 
below with a slight median, longitudinal angularity. 
The medulla occupies about half the inferior length of the brain, 
and posteriorly is considerably higher than broad, angulated both above 
and below, with its greatest diameter at about midheight. Farther for- 
ward its sides are sunken, where the walls of the brain-case are thickened 
in the neighbourhood of the eighth nerve, and its lower surface becomes 
flattened, retaining, how^ever, a slight transverse convexity. 
Measurements of Cast of Brain-cavity of Edmontosaurus (paratype, Cat. No. 2289). 
Mm. 
Length, posterior end of floor of foramen magnum to termination of optic lobes.. . . 262 
Breadth across cerebrum 77 
Anterior height of olfactory lobes 15 
Anterior breadth of olfactory lobes 32 
Height vertically above lower end of pituitary body 98 
