Head.
The head, which-in all animals forms the most important and characteristic part, (see Pl. 10, Figs. 1, 2,) at once shows that the Ichthyosauri were Reptiles, partaking partly of the characters of the modern Crocodiles, but more allied to Lizards. They approach nearest to Crocodiles in the form and arrangement of their teeth. The position of the nostril is not, as in Crocodiles, near the point of the snout; it is set, as in Lizards, near the anterior angle of the orbit of the eye. The most extraordinary feature of the head, is the enormous magnitude of the eye, very much exceeding that of any living animal.[1] The expansion of the jaws must have been prodigious; their length in the larger species, (Ichthyosaurus Platyodon,) sometimes exceeding six feet; the voracity of the animal was doubtless in proportion to its powers of destruction. The neck was short, as in fishes.
Teeth.
The teeth of the Ichthyosaurus (Pl. II, B, C,) are conical, and much like those of the Crocodiles, but considerably more numerous, amounting in some cases to a hundred and eighty; they vary in each species; they are not enclosed in deep and separate sockets, as the teeth of Crocodiles, but are ranged in one long continuous furrow, (Pl. II, B, C,) of the maxillary bone, in which the rudiments of a separation into distinct alveoli may be traced in slight ridges extending between the teeth, along the sides and bottom of the furrow. The contrivance by which the new tooth replaces the old one, is very nearly the some in the Ichthyosauri as in the Crocodiles (Pl. II, A, B, C;) in both, the young tooth begins its growth at the base of the old tooth, where, by pressure
- ↑ In the collection of Mr. Johnson at Bristol is a skull of Ichthyosaurus PIatyodon, in which the longer diameter of the orbital cavity measures fourteen inches.
