STRUCTURE OF LIZARD 697 



numerous impressions made by the epidermic scales, which 

 render it difficult to distinguish the true sutures of the 

 bones. As in Reptiles in general, the brain-case is small 

 in comparison with the skull, and is largely covered by 

 investing bones, between some of which are spaces or fossae. 



Two fused parietals with the rounded median " parietal foramen," 

 two frontals, and the two nasals, are the most important constituents of 

 the roof of the skull. Anteriorly, the premaxillae appear between the 

 nasals, while posteriorly the sickle-shaped squamosal is attached by a 

 suture to the parietal, and is overlapped by one of the two small supra- 

 temporal bones. The orbit is roofed by a series of small bones, of 

 which the anterior and posterior are respectively known as pre- and 

 post -frontal. 



On the floor of the adult skull there is a large basal bone, composed 

 of fused occipital and sphenoidal elements, and continued forward as a 

 slender bar (parasphenoid). This bone gives off two stout processes, 

 the basipterygoid processes, which articulate with the pterygoids. Each 

 pterygoid is connected posteriorly with the quadrate bone of the corre- 

 sponding side, and anteriorly with the palatine. From the union of 

 pterygoid and palatine, a stout os transversum or transpalatine extends 

 outwards to the maxilla. In front of the palatines lie the small vomers, 

 which, in their turn, articulate with the premaxilla and maxilla, both of 

 which are furnished with small pointed teeth. In the posterior region 

 of the skull we have still to notice the large ex-occipitals with which the 

 opisthotics are fused, and which are continued into the conspicuous 

 parotic processes. The lateral walls of the brain-case are largely formed 

 by the paired pro-otics. Internally, an important bone, the epipterygoid 

 or " columella " (not to be confounded with the columella or stapes of 

 the ear), extends from the pro-otic to the pterygoid. The orbit is 

 bounded posteriorly and inferiorly by the jugals. There is no ossified 

 quadrato-jugal, and thus the lateral temporal fossa is open below in the 

 dried skull (contrast Sphenodon). The other fossae of the dried skull are 

 the supra-temporal on the upper surface, and the posterior-temporal on 

 the posterior surface. 



Each half of the lower jaw is composed of six bones, which fuse in 

 the adult. The two rami are sutured to one another in front. 



Limbs and girdles. — In the shoulder-girdle, the flat 

 coracoids, with an anterior precoracoid region, articulate 

 with the sternum, which is represented by a cartilaginous 

 plate of rhomboidal shape. Over it projects the long limb 

 of the T-shaped episternum or interclavicle (a membrane 

 bone), which, at the sides, is continued outwards by 

 the curved clavicles. The remaining elements are the 

 scapulae, w4iich are continuous with the cartilaginous 

 supra-scapulae. 



The fore-limbs have the usual parts. In the carpus all 



