FOSSIL REPTILES. 357 



of greater peculiarity, namely, an orbit surrounded by the ante- 

 rior frontal, the posterior, and the jugal — the temporal united 

 to the tympanic bone, placed at its internal face to furnish 

 the articulation of the lower jaw; the region of the cranium 

 where the concavities for the auricular chamber should be, 

 smooth, and even a little convex, and probably no other auricu- 

 lar osselet than the platina of the stapes. The osteology of the 

 head of any existing animal could scarcely be better known. 



The most striking character in this head is the enormous 

 size of the eye, and the circle of osseous pieces which strengthen 

 the sclerotic in front. These pieces form a character common 

 to birds, tortoises, and lizards, to the exclusion of crocodiles 

 and fish. In fact, in the crocodiles, the sclerotic is simply 

 cartilaginous. In the fish it is often osseous, either in the 

 whole or in part, but never furnished in front with a ring of 

 osseous pieces, as in the birds. This simple character alone 

 is sufficient to approximate this animal to the lizards. 



The total form of the head, and that of many bones, taken 

 separately, announced, as well as the teeth, specific differences 

 in the ichthyosaurus, but the limits of which are not so easy 

 to determine. 



In the head, for instance, which the Baron refers to /. 

 communis, are seen at the root of the nose between the orbits, 

 two angular prominences in front, and between which there is 

 an angular concavity behind. The parietal is more long than 

 broad, and pierced with two oblong holes, one in front, and 

 the other behind, and its temporal crests unite in a single line. 



In another and a smaller head, the parietal is nearly alike, 

 but pierced with only a single hole. Nevertheless, as the 

 teeth are similar, this can only be an accidental difference. 



In another head, on the contrary, the parietal is of equal 

 breadth and length, and altogether flatted behind. There is 

 but a single round hole in front. There are no teeth in this 

 head ; but from the resemblance of the parietal and the sphe- 

 noid to those of a little skeleton which the Baron had already 



