The Dinosaurs of Wyoming - Wyoming State Geological Survey ...

76 THE DINOSAURS OF WYOMING
at the points where they meet the backbone, being thus modified
to support the great weight.
The feet are large, as if adapted to walking in soft sand
or other yielding material. The hand possessed five digits,
while the foot pO'ssessed three well-developed digits, all doubtless
encased in a fleshy pad as in modern elephants.
Teeth are confined to the back of the mouth, as in all
"beaked" dinosaurs. They are small and weak, with wavy
margins. Their food was doubtless very soft, requiring little
mastication.
The brain in this dinosaur is the sm'allest in proportion
to the size of the animal of any known vertebrate, recent or
ancient.
The brain and spinal cord are remarkably interesting in
that curious, nineteen foot armored dinosaur called Stegosaurus
(Figure 21). The internal casts are actually larger
than the central nervous system, because no reptile brain fits
the brain case closely.
The stegosaurian brain is remarkably small, being of less
size than an egg of an English sparrow. The entire cranial
cavity has a length of less than half an inch, a width of about
one-fifth of an inch. The brain cast displaces 56 cc. of water,
and had a total estimated weight of two and one-half ounces.
The total 'weight of the entire animal, in life, must have been
two or three tons at least so that the brain of an elephant is
fifty times the size of the dinosaur.
On the basis of brain weight the stegosaur had no intelligence
at all.
The stegosaur brain has a very large olfactory portion,
small cerebellum, large medulla, and a hypophysis which is
remarkable (Figure 21) not only for its size but also for the
peculiar shape.
As vve go backward along the spinal cord we find two
swellings, intumesences; one at the region of the shoulder,
the brachial enlargement; and the other at the hips, "the sacral
brain." The former is evident for a space of about four joints.
The neural canal in the sacrum is truly astonishing in size,
being more than twenty times the size of the true brain. The
"sacral brain" measures in length 1.14 cm., in width 0.95 cm.,
and displaces 1200 cc. of water.
Professor Lull writes thus of the Armament of this reptile:
"The exoskeleton of Stegosaurus included five types of
structure, of which the first consists of small rounded ossicles
found in one instance in position beneath the throat. The
known armor of the back consisted of four distinct forms of
plates in each of which the dorso-ventral diameter is enor-