156 ROY L. MOODIE 
saurian brain. Osborn is the first one to call careful attention 
to the fact that the so-called ‘brain casts of dinosaurs’ are in 
reality dural casts and as such do not show the anatomy of the 
brain, since in all probability the brain did not fill the dural 
cavity. He based this conclusion on the observations made by 
Dendy on the brain of Sphenodon.?! Professor Osborn has very 
carefully figured the dural casts of the brain cavity of two of 
the largest dinosaurs, one a herbivore, Diplodocus, a member 
of the Sauropoda; the other a carnivore, Tyrannosaurus (figs. 18, 
19). Both had very large hind limbs, but the skulls in the two are 
disproportionate, being very large in Tyrannosaurus and insignifi- 
cant when compared to the size of the body in Diplodocus. If we 
may imagine a mass of flesh and bones of nearly forty tons in 
weight being guided by a head the size of that of a horse, this 
head containing a brain only a fraction the size of the equine 
animal’s, we have a mental picture of Diplodocus (fig. 12). We 
could not expect much cephalic development of the nervous sys- 
tem, and we find but little. Professor Osborn has kindly per- 
mitted me to copy three of his figures and a glance at the brain 
of Diplodocus is very instructive (fig. 18). Additional interpre- 
tations have been made on the figure. The hind limbs of Dip- 
lodocus were very large, attaining a standing height of twelve 
to fifteen feet and the tail was long and heavy. We should 
expect to find a corresponding sacral intumesence lodging a 
‘lumbar brain,’ nor are we disappointed. Professor Marsh 
(81) created considerable interest in the scientific world by an- 
nouncing that the ‘lumbar brain’ of Stegosaurus was ten times 
the size of the cephalic brain. It is certain that the dural cavity 
of the sacrum has ten times the capacity of the cephalic dural 
space (Lull, 1910; Amer. Journ. Sci., vol. 30, pp. 361-377). 
There is, of course, no assurance that the nervous portion of 
the sacral intumesence filled the dural cavity. Doctor Williston, 
who worked out the material of Stegosaurus on which Marsh’s 
original observations were made, tells me that the enlargement 
was largely confined to the sacrum and was not a tapering in- 
24 Dendy, A. 1911. Phil. Trans. Roy. Soc. London, Series B, vol. 201, p. 
227-331. 
