354 FOSSIL REPTILES. 



does not leave, as in the crocodile, a second temporal foss 

 behind the orbit. 



The temporal of the sea-turtle has much analogy with this, 

 both in form and connexions. But in that animal, the mastoid 

 and posterior frontal unite to the parietal above the temporal, 

 to form a vault at the temple, while here, on the contrary, a 

 great vacancy remains, as in the lizards. There is one, also, 

 of variable dimensions in the crocodiles. 



The mastoid is articulated on one part to the posterior 

 frontal and temporal, and, on the other, to the posterior lateral 

 apophysis of the parietal. 



In the lizards, in which it is very small, it is articulated only 

 to the parietal and temporal bones, because the last is inter- 

 posed between it and the anterior frontal. In the crocodiles it 

 is articulated only to the anterior frontal and parietal, because 

 the tympanic is interposed between it and the temporal. But 

 in all those genera it contributes to bear the tympanic bone, 

 and it does the same in the ichthyosaurus. 



The parietal bone of the ichthyosaurus perfectly resembles 

 that of an iguana. The temporal crests approach it like the 

 two branches of an x. Behind it bifurcates into two apophyses, 

 each elevated by a crest, which proceed to the mastoid bones, 

 and attach themselves there to form by their union the poste- 

 rior angle of the temporal foss. On the suture of its junction 

 with the principal frontals, it is emarginated by a large fora- 

 men, which, in certain species, is prolonged into a fissure, 

 over almost its entire length. 



The upper occipital is very like that of an iguana, in the 

 general form, in the large emargination which it has in the 

 lower part for the occipital foramen, in the small one, which is 

 sometimes in the top, for the ligament which united it to the 

 parietal, and in the rough faces which it presents to the lateral 

 occipitals, and to the ossa petrosa. Its external face only is of 

 a more equal convexity. There are two foramina for the 

 vessels, differently situated according to the species. 



