yle for articulation of the neck lies far underneath, at
the base of the frill, almost in the middle of the skull.

[Illustration: Fig. 39.--Skull of _Monoclonius_, a horned dinosaur
from the Cretacic (Belly River formation) of Alberta.
One-fifteenth natural size. The horns over the eyes are
rudimentary, and the nasal horn large, reversing the proportions
in _Triceratops_.]

_Monoclonius, Ceratops, etc._ The _Triceratops_ and another equally
gigantic Horned Dinosaur, _Torosaurus_, were the last survivors of
their race. In somewhat older formations of Cretacic age are found
remains of smaller kinds, some of them ancestors of these latest
survivors, others collaterally related. None of these have the bony
frill completely roofing over the neck as it does in _Triceratops_.
There is always a central spine projecting backwards and widening out
at the top to the bony margin of the frill which sweeps around on each
side to join bony plates that project from the sides of the skull top.
This encloses an open space or "fenestra," so that the neck was not
completely protected above. Sometimes the margin of the frill is
plain, at other times it carries a number of great spikes, like a
gigantic Horned Lizard (_Phrynosoma_).

[Illustration: Fig. 40.--Outline sketch restoration of
_Triceratops_, from the mounted skeleton in the National Museum.]

In _Ceratops_ the horns over the eyes are large and the nasal horn
small. In _Monoclonius_ the nasal horn is large and those over the
eyes are rudimentary. The great variety of species that has been found
in recent years shows that these Horned Dinosaurs were a numerous and
varied race of which as yet we know only a few. Of their evolution we
have little direct knowledge, but probably they are descended from the
Iguanodonts and Camptosaurs of the Comanchic, and their quadrupedal
gait, huge heads, short tails and other peculiarities are secondary
specializations, their ancestors being bipedal, long-tailed, small
headed and hornless.

The fine skulls of _Triceratops_, _Monoclonius_, _Ceratops_ and
_Anchiceratops_ in the Museum collections illustrate the variety of
these remarkable animals. Complete skeletons of the first two genera
are being prepared for mounting and exhibition.

CHAPTER X.

GEOGRAPHICAL DISTRIBUTION OF DINOSAURS.

Remains of Dinosaurs have been found in all the continents, but
chiefly in Europe and North America. Explorations in other parts of