10 FOSSIL REPTILIA OF THE 



the bone is in the form of a subtriangular plate, of 1 inch 7 lines extent along its 

 mesial border, which is slightly concave, receding from its fellow at the medial 

 line, or base, as in the Iguana ; the apex extends outward, and a little downward 

 to abut against the fore and inner part of the ectopterygoid. From the hind 

 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 Saurian dentition is retained in Scelidosaurus. 



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 con- 

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

 the more strongly marked ridge in Ptychognathus 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 believe 

 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 Teleosaur, distinct 

 from the maxillo-lacrymal vacuities. 



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

 Were the super-orbital ossicle in Crocodilia 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 like forward extension and 

 junction with the pre-frontal, but it also passes backward to join the mastoid, 

 leaving to the bone at the back of the orbit a simple post-orbital function. In 

 Scelidosaurus the bone which joins the mastoid also sends down the post-orbital 

 bar to join the malar ; so that I find no nearer approach to the peculiar structure 

 of the upper part of the orbit in Scelidosaurus than the Crocodile would give with 

 a somewhat more fixed and developed superorbital bone. 



The delicate lacrymal bone (73) appears to have been fractured on the left side 



