THE ICHTHYOSAURI A. 211 



nislies the round articular condyle to the first vertebra, and 

 becomes very stout and thick in front. It appears to have 

 been anchylosed neither with the basisphenoid nor with the 

 basi-occipital. The latter bones are adapted to its sides, and, 

 together with the supra-occipital, which is interposed between 

 them above, circumscribe the occipital foramen. The basi- 

 sphenoid, a deep and stout bone, is produced in front into a 

 iong and slender parasphenoidal rostrum. There do not ap- 

 pear to have been any ossified alisphenoids. The parietals re- 

 main separate throughout life ; and, in some species, not 

 merely present a great parietal foramen close to the coronal 

 suture, but are completely divided by a median fissure. Ossi- 

 fied presphenoids and orbitosphenoids appear to have been 

 altogether absent, and the frontal bones are relatively small. 

 The prootic bones are, as usual, situated in front of the ex-oc- 

 cipitals, and between the latter and them there may sometimes 

 be discerned a conical bone with a broad base, which appears 

 to be fitted in between the ex-occipital and the prootic. If 

 this bone were not so large, it miglit well be regarded as a 

 stapes, but it is possible that, as Cuvier suggests, it answers 

 to the separate opisthotic of the Chelonia, 

 . In the naso-premaxillary segment, the nasal bones, con- 

 tinuing the direction of the frontals, attain considerable size, 

 but the premaxillng make up by far the greater part of the 

 snout. The maxillae are reduced, as in birds, to comparatively 

 small and slender rod-like bones, bounding only a fraction of 

 the gape. The vomers are elongated, and situated in the 

 middle line on the underside of the snout. 



The nostrils are small apertures close to the orbits, 

 bounded by the nasal, lachrymal, and premaxillary bones. 



On each side of the frontal there is a large prefrontal, 

 which passes back above to meet the post-frontal, and thus 

 bound the orbit. Below, the maxilla is connected with a 

 jugal. From the post-frontal to the jugal, the posterior mar- 

 gin of the orbit is constituted by a distinct, curved, postorbi- 

 tal bone (Fig. 76, A, I^i. 0). A broad and flat quadrato-jugal 

 ( Q:h) passes from the end of the jugal to the lower end of the 

 quadrate, and covers in the lower and posterior part of the 

 infra-temporal fossa. The space between this bone, the post- 

 orbital, the post-frontal and the squamosal, is occupied by 

 another flattened bone (Fig. 76, A, St.)^ which Cuvier calls 

 the temporal, but which does not appear to have any precise 

 homologue among other Reptilia. The squamosal bone is 

 very large and stout, and forms the postero-external angle of 



