356 FOSSIL REPTILES. 



external ear was more simple in the ichthyosaurus than in the 

 lizards. 



At the internal face of the petrosum is a deep cavity which 

 concealed the vestibulum, and which was closed on the side of 

 the cranium by the upper and external occipitals. In its 

 parietes some remains of semi-circular canals were visible. 



From the mutilation of the lateral occipital and the os 

 petrosum in the Baron's specimens, he was unable precisely to 

 judge whether there had been two fenestrse, or only one. 



He inclines, however, to the latter opinion ; and also thinks 

 that the auricular osselet was reduced to a simple platine, cor- 

 responding to that of the stapes, as it is in the salamander, the 

 siren, and the pro tens. 



The pterygoids form two bands, long, broad and flat, sepa- 

 rated behind by the entire breadth of the sphenoid, and ap- 

 proaching each other in front, a little under the anterior edge 

 of the orbit. They sharpen there into a long point, which is 

 inserted between the palatines, to which it is united by a very 

 oblique suture. They grow wide, laterally towards their mid- 

 dle, probably to give an attachment to the transverse bone, 

 which would appear to join the external posterior extremity 

 of the palatine, and the external edge of which should, in that 

 case, unite, as usual, to the jugal. The posterior extremity of 

 the pterygoids is terminated by a slight enlargement, some- 

 what in a concave arch behind. Neither they nor the pala- 

 tines appear to have had any teeth. 



Such is the general composition of the head of the ichthyo- 

 saurus — a muzzle formed almost entirely by the intermaxil- 

 laries ; the maxillaries thrown to the sides of its base, the 

 nasals to the upper face of this same base, the nostrils pierced 

 between the nasals, the intermaxillaries, and the anterior 

 frontals ; the frontal, the parietal, the occipital, the ossa 

 petrosa, the sphenoid, the pterygoids, pretty nearly the same 

 as in the lizards, especially as in the iguanas. 



But in the region of the ear and temple are some characters 



