206 REPTILIA. 



a sharp median crest, and the quadrate forms a remarkably deep pedicle. 

 There are small supraorbital bones above the eye, but no sclerotic plates 

 have been observed. Each ramus of the mandible comprises at least six 

 elements and exhibits a slender coronoid process behind ; the preden- 

 tary bone is crescentic, with a regularly jagged margin which seems to 

 have been ensheathed in a horny beak. The premaxilla is also toothless, 

 but the maxilla and dentary bear closely arranged stout grinding teeth. 

 All the teeth, when unworn, are of the form shown in the accompanying 

 fig. 127 ; when worn they are reduced to a flattened stump. They are 

 fixed in separate incomplete sockets in very close order, the successional 

 teeth well-formed below those of the functional row ; the crowns of the 



FIG. 125. 



Iguanodon bernissartensis; restoration of skeleton by 0. C. Marsh, one-eightieth 

 nat. size. Wealden ; Bernissart, Belgium. 



upper teeth are a little inclined inwards to meet those of the lower jaw 

 which are similarly inclined outwards. The vertebral column comprises 

 more than 80 vertebrae, 10 being cervical, 18 dorso-lumbar, from 4 to 6 

 sacral, and the remainder caudal. The vertebral centra are solid ; and 

 those of the cervical and apparently anterior dorsal regions are opistho- 

 coelous, while those beyond are only slightly amphiccelous. All the cervical 

 vertebrae except the atlas bear ribs, and there are only one or two lumbar 

 vertebrae destitute of them ; separate short ribs also appear at least on 

 the anterior 13 caudal vertebrae. The proximal ends of the chevron bones 

 are united by a delicate bridge, and are placed intervertebrally between 

 the 3rd and about the 36th caudal vertebrae. In the pectoral arch, the 



