268 PALEONTOLOGY. 



tympanic (28) is a broad deep plate of bone, convex out- 

 wardly. 



The zygomatic arch is continued forward from the tym- 

 panic (28), to the postorbital boundary (26); it is large and 

 deep, and from its outward curvature, gives great width to 

 the fossae which lodged the temporal muscles. The orbits 

 are of a subtriangular form; their aspect is more upward 

 than outward. The post- and pre- frontals unite above 

 the orbit, and contribute a narrow tract to each side of 

 the interorbital space, which is flat. The nostril (n) is single, 

 terminal, and vertical; it is bounded laterally by short pre- 

 maxillaries. 



The most interesting peculiarity in the skull is the well- 

 marked definition from the other teeth, by a contrasted supe- 

 riority of size, of an upper and lower canine tooth on each 

 side, having the same position in the skull and relative 

 position to each other as in the carnivorous mammals. In 

 no other Saurian are incisors so divided from molars by a 

 single canine ; in none is such definition of the three kinds of 

 teeth so plain and unequivocal. 



The premaxillaries contain each four equal-sized teeth 

 with simple conical crowns, much shorter than the canines, 

 sloping a little forward from the vertical position, and passing 

 in front of the lower incisors when the mouth is shut. The 

 eight lower incisors are narrower than those above, but have 

 about the same length of crown. Both upper and lower in- 

 cisors are arranged in contact, or close order, as in mammals. 

 The canines, c c, have the same relative position to each 

 other as in mammals, the lower passing in front, and on the 

 inner side of the upper, when the mouth is shut. Twelve 

 close-set conical subcompressed teeth succeed the canine in 

 both jaws, holding the place of the molar series ; they are 

 of nearly equal size, but much less than the canines ; those 

 of the upper jaw pass external to the lower molars, when the 



