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. | | | | | |Superior molars. | | | | | | |Zygapophyses. | | | | | | | |Brain. | | | | | | | | Pliocene. |1-1, 2-2 | |Digitigrade. (Plantigrade.) | | |Grooved. (Flat.) | | | |Interlocking. (Opposite.) | | | | |Faceted. | | | | | |4-tubercles, crested and cemented. | | | | | | |Doubly involute. Singly involute. | | | | | | | |Hemispheres larger, convoluted. | | | | | | | | Upper Miocene. (Loup Fork.) |3-3, 4-4, (5-5) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Middle. (John Day.) |2-2, 3-3, 4-4 | |Digitigrade. | | |Grooved. | | | |Interlocking. | | | | |Faceted. Smooth | | | | | |4-tubercles, and crested | | | | | | |Singly involute. Double involute. | | | | | | | |Hemispheres larger, convoluted. | | | | | | | | Lower (White River.) |3-3, 4-3 | |Digitigrade. Plantigrade. | | |Grooved. | | | |Interlocking.