LIASSIC DINOSAURS. 95 



border near the base a long and narrow process is sent off to abut against the 

 tympanic. There is no trace of teeth on the pterygoid, as in the recent Iguanas ; 

 the higher type of Sam-ian dentition is retained in Scelidosauriis as in Iguanodon 

 (PI. 60, fig. 5, 20, 24). 



The hind and probably main part of the maxillary, here preserved, is chiefly 

 remarkable for the horizontal ridge which nearly equally divides the outer or 

 facial plate of the bone into an upper and lower facet ; and this ridge is 

 continued a little way below the orbit upon the malar bone. It corresponds 

 with the more strongly marked ridge in Pti/chognathus and Oudenodon} There 

 is a lower and slighter longitudinal prominence of the maxillary along the outer 

 alveolar plate. The maxillary reaches back beyond the middle of the orbit, from 

 which it is separated, as in other Saurians, by the malar and lacrymal bones. 



On both sides there is a small, unossified space between the maxillary and 

 lacrymal ; this corresponds with the larger vacuity in that part of the bones of 

 the face in the Pterodactyle, which is reduced to the present proportions in some 

 Teleosaurs, and becomes the functional nostril in the Ichthyosaur ; but I beheve 

 that the true external nostrils of Scelidosaurus were included in the fore part of 

 the skull which has been broken away, and were, as in the Teleosaiir, distinct 

 from the maxillo-lacrymal vacuities. 



The orbits of Scelidosaurus are subcircular, almost vertical, looking outward. 

 Were the super-orbital ossicle in Grocodilia enlarged and fixed by suture in the 

 upper scoop of the orbit, it would give a less vertical outlook to the eye than it 

 usually presents, especially in the skull of a crocodile from which that ossicle has 

 been removed. But the composition of the rim of the orbit in Scelidosaurus is 

 open to other homologies. The bone (71) may be compared with that wedged 

 into the upper and back part of the orbit in some lizards, between the frontal 

 and post-frontal, and by Cuvier regarded as a dismemberment of the latter 

 element ; only in Scelidosaurus it is extended forward to the pre-frontal, excluding 

 the frontal from the orbit. In Ichthyosaurus the post-frontal has a forward 

 extension to junction with the pre-frontal ; it also passes backward to join the 

 mastoid, leaving to the bone at the back of the orbit (PI. 20, fig. 1, 12) a simple 

 post-orbital function. In Scelidosaurus the bone which joins the mastoid sends 

 down a post-orbital bar (PI. 40, 12) to join the malar (ib. 20). The post- 

 frontal holds the same relations to the orbit in Iguanodon (vol. i, p 521, PL 49, 

 fig. 9, 12). In both genera there is a masto-post-frontal zygoma, as well as the 

 ordinary malo-squamosal one. But the intervening space is not walled over by a 

 supplementary plate as in Ichthyosaurus (PI. 20, fig. 1, 27^) 



The delicate lacrymal bone (Pis. 45, 46, 73) appears to have been 



1 ' Description of the Fossil Eemaiua of the Eeptilia of South Africa,' 4th, 1876, vol. i, pp. 

 48 — 56 ; vol. ii, pis. xlv, Iv. 



