THE 
AMERICAN NATURALIST 
Vou. XXXII. February, 1898. No. 374. 
THE SIGNIFICANCE OF CERTAIN CHANGES IN 
THE TEMPORAL REGION OF THE 
PRIMITIVE REPTILIA. 
E. C.-CASE. 
CERTAIN “mutations ” or lines of definite evolution seem at 
the present time to be well established in the various mamma- 
lian phyla. Typical of such lines are the changes involved in 
the development of the Perissodactyla and Artiodactyla from 
the pentadactyl forms of the Eocene; the development of the 
complicated carnivorous and herbivorous molar teeth from the 
simple tritubercular type and the gradual assumption of 
the molariform condition by the premolars of the herbivorous 
forms. Around such persistent lines of development have 
gathered the minor changes or “variations ” determining the 
various genera and species. 
As yet there has been no recognition of such a line of defi- 
nite evolution among the Reptilia, but it is the belief of the 
author that such a line can be demonstrated. The series 
of changes alluded to are those involved in the development of 
the temporal region of certain of the Permian Reptilia. Closely 
connected with this series are other changes, such as the 
gradual*assumption of the tuberculate condition of the teeth 
and the introduction among the tarsal bones of a calcaneum. 
