CHAPTER I 



THE SKULL OF REPTILES 



External Appearance, Excrescences, and Chief Openings 



The 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; in- 

 sectivorous reptiles may have a more slender skull (Fig. 52 b); 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 protu- 

 berances. 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 a) 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 cha- 

 meleons in the development of facial horns (Fig. 55 d), 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 



