358 FOSSIL REPTILES. 



referred to /. tenuirostris, he is inclined to refer this head to 

 the same species. 



In a fourth head the parietal was flat and short, but the 

 round hole in front is continued by a fissure which is widened 

 behind into a second hole. The Baron refers this to /. inter- 

 medius. 



Lastly, in the hinder portion of a head, as large as the first- 

 mentioned, the parietal is equally elongated, and without a 

 hole. This M. Cuvier refers to /. platyodon. 



There are other differences observable in the sphenoid, but 

 it is needless to insist upon them here. 



The lower jaw of the ichthyosaurus, equally elongated and 

 pointed at the muzzle, is formed of two branches, which ap- 

 proach each other without curving much, and which are sym- 

 physized on a little more than half of their length. Each 

 branch is composed of six bones, as in all the lizards and cro- 

 codiles, but somewhat differently disposed than in either of these 

 families. 



Neither at the external nor internal face of the jaw are 

 observable the two large holes which are seen in the cro- 

 codiles. 



The dentary bone forms its external face from the point as 

 far as under the middle of the orbit. 



The opercular occupies the lower edge and the internal face 

 of the jaw almost on an equal space, penetrating into the sym- 

 physis almost to its point. 



The angular and subangular share the external face at the 

 posterior part. 



To the sub-angular belongs the coronoid apophysis, contrary 

 to the arrangement in the lizards, and conformably to what is 

 seen in the crocodiles. This coronoid apophysis is small, and 

 very obtuse. 



The complementary bone is very small, and thrown to the 

 external face of the jaw, as in the crocodile. 



The articular is not considerable, and its greatest extent is 

 at the external face, as in the crocodile. 



