ew. The small italics throughout signify the
following homologous parts: _m_, medulla; _cb_, cerebellum; _op_,
optic lobes; _cr_, cerebrum and thalamus; _ol_, olfactory lobes. The
series shows a progressive consolidation and enlargement of the
brain in general, and of the cerebrum and cerebellum in particular,
which likewise exhibit continually advancing structure in respect of
convolution. In the case of Man, these two parts of the brain have
grown to so great a size that they conceal all the other parts from
the superficial points of view represented in the diagram.]

[Illustration: FIG. 87.--Ideal section through all the above stages.
(After Le Conte.])

The tabular statement on the following diagram, which I borrow from
Prof. Cope, will serve at a glance to reveal the combined significance
of so many lines of evidence, united within the limits of the same group
of animals.

To give only one special illustration of the principle of evolution as
regards the skull, here is one of the most recent instances that has
occurred of the discovery of a missing link, or connecting form (see
Fig. 88). The fossil (B), which was found in New Jersey, stands in an
intermediate position between the stag and the elk. In the stag (A) the
skull is high, showing but little of that anterior attenuation which is
such a distinctive feature of the skull of the elk (C). The nasal bones
(N) of the former, again, are remarkably long when compared with the
similar bones of the latter, and the premaxillaries (PMX), instead of
being projected forward along the horizontal plane of the base of the
skull, are deflected sharply downward. In all these points, it will be
seen, the newly discovered form (_Cervalces_) holds an intermediate
position (B). "The skull exhibits a partial attenuation anteriorly,
the premaxillaries are directed about equally downward and forward, and
the nasal bones are measurably contracted in size. The horns likewise
furnish characters which further serve to establish this dual
relationship[18]."

[18] Heilprin, _Geological Evidences of Evolution_, pp. 73-4 (1888).

[Illustration: FIG. 88.--Skulls of--A, Canadian Stag; B, _Cervalces
Americanus_; and C, Elk. (After Heilprin.)]

Formation.
|No. of toes
| |Feet
| | |Astragalus.
| | | |Carpus and tarsus.
| | | | |Ulno-radius.
| | | | | |S