FJG. 55. Diagrams of skulls, showing especially the composition of the bony arches of 

 the orbito-temporal region. 



L, PYTHONOMORPHA. Clidastes, p. 490. 



M, N, 0, LACERTILIA, p. 496. M, Varanus, p. 543 ; N, Uromastix, p. 524 ; O, 



Lacerta, p. 550. 



P, ICHTHYOSAURIA, p. 479. Ichthyosaurus, p. 483. 

 Q, PTEROSAURIA, p. 484. Dimorphodon, p. 486. 

 R, AVES, generalised, for comparison. 

 S, MAMMALIA, generalised, for comparison. 

 T, OPHIDIA, p. 581. 



C, Condyle of mandible ; Col, columella cranii ; F, frontal ; 7, interparietal or 

 pineal foramen ; l.A, Inner angle of mandible ; /, jugal, shaded vertically ; 

 L, lacrymal ; j/, maxillary ; JV, nasal groove ; Na, nasal bone ; 0, orbit ; 

 Oj, preorbital fossa ; P, parietal : P/, postfrontal ; Pra, premaxillary ; Pr, pre- 

 frontal ; Ptg, pterygoid ; Q, quadrate ; Qj, quadrate - jugal ; Sq, squamosal, 

 shaded obliquely ; St, supratemporal bone. 



