256 EXTINCT MONSTERS 
these elevations, or horn-cores, has, of course, been preserved ; yet 
a fortunate discovery may perhaps reveal their nature by the 
form of a natural cast, as the eyeball of the Oreodon is sometimes 
thus clearly indicated in the fine Miocene matrix which envelops 
these animals.” It looks rather as if we have here an early stage 
in the evolution of horns, and it may be that in the course of 
subsequent ages such prominences as those developed into true 
“horn cores,” such as sheep or goats have, while the thick bosses 
of skin that covered them slowly developed into the true horns 
that are attached to these cores. If this is so, then we have here 
another instance of a “generalised” structure. Again, the limbs 
with their five toes tell us at once that the creature’s place in 
Nature is outside of those two great groups of modern ungulates, 
or hoofed quadrupeds, the odd-toed and the even-toed, represented 
on the one hand by the horse, rhinoceros, and tapir, on the other 
by the pig, camel, deer, ox, and many other forms. Probably the 
two groups had not at this early period branched off from the 
primitive ungulate stock with five toes in each foot, of which 
the elephant is a living descendant, and from which also the 
Dinoceras must have come. 
The limbs were strong and massive, but the brain was 
remarkably small, so that our Dinoceras cannot be credited with 
any high degree of intelligence: and here again we see an 
absence of “ specialisation ” compared with the sagacious elephant. 
Professor Marsh has taken casts of its brain-cavity (see Fig. 96). 
These casts show that the brain was smaller (in proportion to 
the size of the animal) than in any other mammal, whether living 
or extinct—and even less than in some reptiles! In fact, it was 
a decidedly reptilian kind of brain, Perhaps it may seem hardly 
credible, bu& so small was the brain of Dinoceras mirabile, that 
it could have been pulled through the apertures (neural canal) 
