SKULL — REPTILES 



139 



ethmoid region. Most of the extinct orders (Dinosaurs and Ptero- 

 saurs excepted) and Rhynchocephals and lizards have a parietal 

 foramen for the parietal eye between the two parietals.^ 



The nasals (fused in some lizards and lacking in all Chelonia 

 except Chelys and its alhes, figure 147) vary in length with that of the 

 snout, reaching the extreme in Crocodilia and Ichthyosaurs. Usu- 

 ally they extend to the nares and form part of the nasal septum, being 

 met in the median line by the ascending processes of the premaxillae. 

 The orbit is bounded by several bones. In front is the more median 

 prefrontal- (in turtles replacing the nasal) and lateral to this in many 

 hzards is a lacrimal. The posterior border 

 is composed of postfrontal and usually a 

 postorbital, the latter occurring in recent 

 groups only in Squamata and Sphenodon. 

 Lacertilia, Ichthyosaurs, Python and some 

 Dinosaurs n\ay have one or more supra- 

 orbitals, while some lizards have other 

 bones on the lower and posterior sides of 

 the orbit. Several extinct groups (Pyth- 

 onomorphs, Ichthyosaurs, Plesiosaurs, 

 some Theromorphs and Pterosaurs) may 

 have sclerotic bones. 



As a rule the lateral margin of the cra- 

 nium consists of premaxilla, maxilla, zygo- 

 matic and quadratojugal, the latter 

 reaching the squamosal, which to a 

 greater or less extent overlies the quad- 

 rate at or near the posterolateral angle 

 of the cranium. In the lower extinct 

 orders a supratemporal often occurs between parietal and squa- 

 mosal, and behind this, on the posterior margin of the cranium 

 a tabulare (so-called epiotic). The tabulare often appears in the 



Fig. 147. — Cranium of Hydro- 

 medusa ( Jaekel, ' 1 1 ) . /, frontal ; 

 /, prefrontal; m, maxilla; n, 

 nasal; oo, opisthotic; os, supra- 

 occipital; p, parietal; po, post- 

 orbital; pr, prootic; pt, ptery- 

 goid; q, quadrate; 55, squamosal; 

 V, vomer; s, zygomatic. 



^ Occasionally the parietal foramen is farther forwards , in the median Hne, even 

 between the frontals. A few Theromorphs have an interparietal bone between the 

 parietals and the supraoccipital. The parietals are fused in Crocodilia and most 

 Squamata, the frontals also in the former. 



- Watson has shown that the lacrimal of Nytliosauriis and Diademodon is so closelj' 

 similar to that oi Peramelcs (mammal) that Gaupp's contention that the mammal lacri- 

 mal is the reptilian prefrontal will not hold. Gaupp called the reptilian lacrimal the 

 adiacrimal. 



