the Homologies of the Lizard's S/cuU. 91 



specimen of Pleurosaui'us f/oldfussi, which lias been for many 

 years in the British Museum, lias recently been more fully 

 developed, and now shows in perfect preservation the whole 

 structure of the upper and lateral surfaces of the skull 

 (PI. VI.). 



The skull is comparatively little crushed for a Solenhofen 

 Slate specimen, and, althougli the bones are much cracked, 

 the sutures arc very easily identified. The specimen is a 

 skeleton lacking the greater part of the tail, and is exposed 

 from the dorsal surface. 



The skull is elongated and depressed, the orbits are large, 

 as is usual in lizards, and the single temporal fossa rather 

 small. The length of the head depends on the great pre- 

 orhital extension, which results iu the formation of very 

 large bony external nares, looking upwards and outwards, 

 and only separated by narrow processes of the nasals — these 

 lie very far behind the anterior end. 



The physiognomy of the preorbital part of the skull is 

 very like Vuranus, and its structure is as follows : — 



The premaxilke (P.Mx.) are massive bones, meeting in a 

 long suture on the dorsal surface, but posteriorly separated 

 by the nasals. Their anterior ends are depressed, and each 

 seems to carry one blunt tooth (the exposure of the speci- 

 men makes this not quite certain). The long outer faces 

 are covered by the maxillse, and the posterior border forms 

 the front edge of the external nares. Each bone has a 

 curious foramen opening into its dorsal surface. 



The maxilla (Mx.) is a very large bone. The lower border 

 is nearly straight, and is shown by other specimens to bear a 

 single row of bluntly pointed acrodont teeth, the last of 

 which is exposed in the British ]\Iuseum specimen. The 

 anterior part of the maxilla overlaps the outer face of the 

 premaxilla wiih a thin squamous edge ; behind this its upper 

 border is slightly depressed and smoothly rounded, forming 

 the outer border of the nostril. It then again becomes 

 squamous and overlaps the prefrontal and lachrymal until it 

 drops down to form part of the lower margin of the orbit ; 

 finally, it is covered above and without by the jugal. 



The nasal (Na.) is a large bone which has a long median 

 suture with its fellow ; its anterior edge is in contact with 

 the premaxilla, and the part of the bone between the nares 

 is a very narrow rod ; posteriorly it expands and forms a 

 considerable area of the top of the head, its lateral border 

 being in contact with the prefrontal and its posterior end 

 with the frontal. 



The prefrontal (Pr.Fr.) is a large bone whose anterior border 



