ORDER ICHTHYOPTERYGIA. 



121 



maxillae in the upper jaw ; and the nares are consequently approxi- 

 mated to the orbit, which is of very large size, and has a ring of 

 bony plates in the sclerotic ; there is a large parietal foramen j and 

 there are two temporal arcades connected together by the supra- 

 temporal (prosquamosal or supraquadrate), which roofs over the 

 infratemporal fossa, after the Labyrinthodont fashion. Other char- 



Fig. 1024. — Reduced left lateral view of the skull of Ichthyosaurus intermedins ; from the 

 Lower Lias of Dorsetshire. P»i.v, Premaxilla ; Mx, Maxilla ; X, Nares ; La, Lachrymal ; 

 Prf, Prefrontal ; Fr, Frontal ; Pa, Parietal ; Pt, Postfrontal ; St, Supratemporal ; Sq, Squa- 

 mosal ; Qj, Quadratojugal ; Qu, Quadrate; Jzi, Jugal ; Pt.O, Postorbital. (After Huxley.) 



acteristic features of the skull are the small frontals ; the presence 

 of an opisthotic in the occipital region ; the distinctness of the post- 

 orbital from the postfrontal, and of the lachrymal from the pre- 

 frontal ; the firm fixture of the quadrate, which does not, however, 

 suturally unite with the pterygoid ; and the presence of a foramen 

 separating the middle portion of the quadratojugal from that bone, as 



Fig. 1025. — The centrum of an anterior dorsal vertebra of Ichthyosaurus, viewed in section, 

 and from the anterior and left lateral aspects ; from the Kimeridge Clay of Wiltshire. Reduced. 

 (After Owen.) 



in the existing Rhynchocephalian genus Sphenodon, and the presence 

 of a columella, or epipterygoid. The palate has essentially the same 

 structure as in the last-named genus. As in the Squamata, there is 

 no lateral vacuity in the mandibular rami. The teeth are confined to 

 the jaws, and are implanted in a continuous groove, without anchy- 

 losis to the bone. Their crowns are sharply pointed, and are usually 



