Page:The Osteology of the Reptiles.pdf/27



skull of reptiles, as of other vertebrates, has undergone many changes in adaptation to food, offensive and defensive habits. It has lost not a few bones in various forms, and others have united or formed new associations; to such an extent, indeed, that there are several in later reptiles about whose homologies there has been and yet is dispute. It has developed excrescences or horns for defense or offense, or has been covered at times with a solid armor of skin bones; but it has gained permanently no new bones, though a few have been added temporarily from the exoskeleton. The skull of carnivorous reptiles (Figs. 33, 45) is more or less elongate, like that of a wolf; insectivorous reptiles may have a more slender skull (Fig. 52 ); while those reptiles using the jaws to crush invertebrates always have a short and powerful skull (Fig. 49). The face of aquatic, fish-eating reptiles (Fig. 58) is always long, sometimes very long (Fig. 67), as in the modern gavials.

Excrescences or horns on the skull have been developed in not a few. The earliest known is that of the cotylosaurian Chilonyx, with excrescences, and the theromorph Tetraceratops, with large protuberances. Some of the later Cotylosauria, like Elginia, had horny protuberances at the back part. A few carnivorous dinosaurs have a median facial and supraorbital rugosities, as though for the support of horns or spines. In the Ceratopsia (Fig. 70 ) the development of horns and spines was carried to a remarkable degree, not only on the face but also along the posterior margin of the greatly extended skull. Perhaps of all reptiles none has surpassed some of the modern chameleons in the development of facial horns (Fig. 55 ), though not a few other lizards, like the horned lizards and moloch lizards, have many sharp protuberances and horny excrescences, which, were they magnified to the size of dinosaurs would be equally imposing. Even some turtles, like the southern Miolania, have horns upon the skull. Usually the median unpaired facial horn is borne by the