FOSSIL REPTILES. 293 



very projecting and more forward, the lower angle of the jaw 

 being more forward^ and the dentary part shorter in proportion. 

 It is not necessary here to enter into a detailed description of 

 these six bones, nor of their variations, and those of the jaw 

 in the different subgenera. 



But the teeth cannot be passed over without notice. They 

 are not in alveoli, like those of the crocodiles, and those which 

 should replace them are not produced in their cavities. The 

 gelatinous nuts of the teeth adhere to the internal face of the 

 dentary bone, without having any osseous partitions between 

 them, and sometimes without being protected on the internal 

 side by a lamina of this bone. Their bases are therefore 

 separated from the cavity of the mouth only by the gum. 

 This basis is not divided into roots ; but when the tooth has 

 arrived to its full growth, the same phenomenon occurs as in 

 the fish. The gelatinous nut becomes ossified. It unites 

 intimately, on one side, to the boneof the jaw, contracting, on 

 the other, a close adherence with the tooth which it has ex- 

 uded. The tooth then appears as a prominence, an apo- 

 physis, in fact, of the jaw, only that it is covered with enamel; 

 but its base is naked and purely osseous, and around this base 

 are seen striae, and little pores, through which the vessels have 

 penetrated, or are still penetrating, into its interior cavity, and 

 which also mark the place where the rupture will be made 

 when this tooth shall yield its place. 



The new teeth spring, not in the cavity of the old, and pass- 

 ing through them, as in the crocodiles, but near the internal face 

 of their basis, or, in certain species, in the thickness of the 

 bone, above or below this basis, according to the jaw. In 

 this last case a cavity is formed in the bone, which lodges, 

 for a certain time, the pulpy nut and the cap which springs 

 above it. This cavity opens by degrees to the internal face 

 of the dentary bone. In the other way the pulpy nut is 

 simply developed under the gum ; but in proportion as the 

 dentary cap grows, it often forms for itself a notch in the base 



