51 
of the passage is large and close behind the internal auditory meatus, 
the external one is much smaller and opens under the ridge already mention- 
ed about 9 mm. distant from the back margin of the fenestra ovalis. The 
lower opening is for the transmission of the jugular vein. The passage for 
this vein starts within the wall of the brain-cavity in a small orifice well 
down in the medullary region some distance beneath the inner end of the 
foramen lacerum posterius. It curves upward and backward through 
the bone and emerges close beneath the common exit of the ninth, tenth, 
and eleventh nerves, separated from it only by a thin partition of bone 
so that the two openings are almost confiuent externally. Near the external 
end of the jugular passage there seems to be a branch leading forward 
within the bone, but it is small and its course has not been ascertained. 
The opening behind the foramen lacerum posterius, and distant from it 
about 8 mm., is the anterior condyloid foramen. Figures 26 and 27, a, c, f. 
The hindmost of the foramina, about 16 mm. farther back, is the exit of 
the twelfth or hypoglossal nerve (XII). Its inner end is considerably 
larger than the outer one. 
Brain. {Figure 27.) 
The brain-cavity of Edmontosaurus is long and narrow but relatively 
much broader across the cerebrum than elsewhere. Its length is slightly 
less than one-fourth that of the skull, and it is both actually and porpor- 
tionately longer than the brain-cavity of Claosaurus annectens as repre- 
sented by Marsh’s figure of the cast. 
In the paratype of Edmontosaurus there is little distortion in the 
cranium and an accurate gelatine cast of the entire brain-cavity was obtain- 
ed and reproduced in plaster. Figure 27, A, C. The cast includes the 
nerve exits for their full extent outward, giving the diameter, direction, 
and length of the passages, and the thickness of the walls of the brain- 
case at any particular opening. 
The shape of the brain-cavity probably does not give exactly that of 
the brain itself especially if conditions were at all similar to those found 
in the Tuatara {Sphenodon punctatus) of New Zealand. Dendy^ has 
remarked on the great disparity in size in Sphenodon between the brain- 
cavity and the brain, which latter he found to be suspended in the cavity 
by innumerable strands of connective tissue. It is reasonable to suppose, 
however, that in dinosaurs the brain conformed in a moderate degree 
to the shape of the cavity, and this assumption appears to be borne out 
by the cast in which the various divisions of the brain seem to be fairly 
represented as regards size and relief. In describing the cast of the brain- 
cavity of Edmontosaurus^ therefore, its different parts will be referred 
to in terms that would be applied to the brain itself. 
In Figure 27, the cast is shown in lateral. A, superior, B, and inferior, 
C, aspects. In it the principal divisions of the brain are denoted, viz., 
the olfactory lobes, the cerebrum (cerebral hemispheres), the optic lobes, 
the cerebellum, the medulla oblongata, and the pituitary body. All the 
cranial nerve exits are represented, as well as the internal carotid artery’s 
entry into the pituitary body from below. Two constrictions are con- 
iPhilos. Trans. Royal Soc. London, Ser. B. vol. 201, 1911, pp. 227-331. "On the structure, development, and 
morphological interpretation of the pineal organs and adjacent parts of the brain in the Tuatara (Sphenodon punC' 
talus,” by Arthur Dendy. 
