SKULL REPTILES 



165 



except that the exoccipital is fused with the opisthotic, forming a 

 strong parotic process. Parietals and frontals are short and there 

 is no parietal foramen. The orbits are far posterior, the nares nearly 

 terminal, and confluent in some species. The orbits are closed 

 behind by a process from the zygomatic to the postf rontal. The older 

 fossils have an antorbital vacuity bounded by maxilla and nasal, 

 but this is united with the orbit in recent genera. The zygomatic 

 arch is complete, the zygomatic bone reaching the quadratojugal. 



The cranial floor varies. All have the choanae posterior to the 

 primitive position, the older groups having a palate formed by the 



Pf^ 



r' 



ttlx 



pmx I 



%ip '^ 



.>nf -sc -M 'i 



fi^l^^ 



d 



U}} 



Fig. 177. — Skull of Caiman lalirostris (Reynolds, '97). an, angulare; art, articulare; 

 CO, coronoid; d, dentale; eo, exoccipital; /, lacrimal; mx, maxillary; pf, postfrontal; pi. 

 palatine; pmx, premaxilla; pt, pterygoid; q, quadrate; qj, quadratojugal; sa, surangulare; 

 sq, squamosal; tr, transversum; s, zygomatic. 



palatal processes of maxillae and premaxillae, the choanas at its 

 hinder margin, separated by the postero-lateral parts of the vomers. 

 In Telosaurus, etc. the palatines meet, carrying the choana? farther 

 back. The next step is the covering of the vomers (Goniopholis, etc.) 

 by the palatines and the meeting of the anterior ends of the ptery- 

 goids. In existing genera the pterygoids have met so far back that 

 the vomers and the anterior end of the basisphenoid are covered, and 

 the choanas are near the posterior end of the cranium (fig. 178), the 

 vomers now being thin plates between the nasal passages. In older 

 Crocodilia the Eustachian tube lies in a groove on the ventral side 

 of the basisphenoid; in recent species, the grooves of the two sides 

 close to tubes with a common opening behind the posterior end of the 



