2 9 o COMPARATIVE ZOOLOGY OF CHORDATES 



in the roof of the temporal cavity, it is not an opening into the 

 brain-case. 



Some reptiles have a single temporal fossa on each side. 

 Others have a pair on each side, for which reason they are 

 called the Diapsida. The Diapsida have a superior and an 

 inferior temporal fossa, and these fossae are separated from the 

 orbit by the post-orbital bar (usually formed by the post- 

 frontal and post-orbital bones) ; they are separated from the 

 post-temporal fossa by the post-temporal bar (supratemporal 

 and squamosal bones) ; and they are separated from one 

 another by the superior temporal bar (post-orbital and squa- 

 mosal bones. The superior temporal fossa is bordered above 

 by the parietal bone ; the inferior temporal fossa is bordered 



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 Fig. 140. — Left side view of a skull of a bird (Columba). 



below by the inferior temporal bar (jugal, quadrato-jugal, 

 and squamosal bones). 



The Diapsida include the Rhynchocephalia of which 

 Sphenodon is an example, the Crocodilia, the Dinosauria, the 

 Pterosauria, and the birds. In the latter, however, the post- 

 orbital and temporal bars have been broken, with the result 

 that the temporal fossae can no longer be clearly recognised. 

 It can nevertheless be seen that the bird's skull must have 

 been derived from a Diapsid type which had the typical two 

 temporal fossae. In the primitive crocodiles, in the Pterosaurs, 

 Dinosaurs, and birds, there is also a prelachrymal fossa on each 

 side, between the orbit and the nostril. The condyle is usually 

 single in the Diapsida. 



