Page:Popular Science Monthly Volume 73.djvu/569

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The family of the high-spined Pelycosaurs did not monopolize the wonders of the reptilian horde; however the borders of the streams, the swamps and the uplands, harbored other forms whose structure is just beginning to be understood. One group of these, called by Cope the Cotylosauria, is the most primitive of the reptiles and the nearest to the amphibians. These animals were low-bodied and sprawling, with a head completely roofed over by bone and showing between the orbits the third, or pineal, eye. Rudiments of this third eye are still present in the human brain, the pineal gland between the cerebrum and cerebellum, and in many of the modern lizards it is still so far functional as to have a rudimentary retina perhaps capable of perceiving light.

Another group of reptiles closely resembling the Cotylosauria in outward appearance, but differing in many details, notably the development of a body armor, were placed by Cope in a separate order, the Chelydosauria. As indicated by the name, the Chelydosauria are probably the ancestors of the turtles. Aside from more technical points this relationship is shown by the development of a more or less complete carapace. The skeleton of the larger forms is pretty well known and the general shape is shown in the restoration of the skeleton of Diadectes, Fig. 11. The teeth are elongated transversely and flattened, telling of a purely vegetable diet; the dermal armor consisted of five overlapping plates on each side lying on the first five dorsal ribs; the anterior one is small, the second much larger and the last three smaller again. In certain small forms, Otocæeus and Conodectes, the armor was much more perfect, consisting of strong dermal plates corresponding