canine teeth in the upper jaw, though they are absent in the moose, in
the distinctively American type and a few others. The cleaned skull
always shows a large vacuity in the outer wall in front of the orbit,
which prevents the lachrymal bone from reaching the nasals. No deer has
a gall bladder. There are many other distinctions, but as all have
exceptions they are of value only in combinations.

The earliest known deer, belonging to the genus _Dremotherium_, or
_Amphitragulus_, from the middle Tertiary of France, were of small
size and had four toes, canine teeth and no antlers. Their successors
seem to have borne simple forked antlers or horns, probably covered with
hair, and permanently fixed on the skull. Very similar animals existed
in contemporaneous and later deposits in North America. From this point
the course of progress is tolerably clear as to deer in general,
although we are not sure of all the intermediate details--for it must
not be forgotten that a series of types exhibiting progressive
modifications in each succeeding geological period is quite as
conclusive in pointing out the genealogy of an existing group as if we
knew each individual term in the ancestral series of each of its
members. Thus we do not yet know whether the peculiar antler of the
distinctively American deer, of the genus _Mazama_, is derived from
an American source or took its origin in the old world, for the fossil
antlers known as _Anoglochis_, from the Pliocene of Europe, are
quite suggestive of the _Mazama_ style, but as nothing is known of
the other skeletal details of _Anoglochis_, any such connection
must at present be purely speculative, but the element of doubt in this
special case in no way disturbs the certainty of the general conclusion
that all our present _Cérvidae_ have come through distinct stages
in the successive periods, from the simple types of the middle Tertiary.