484 PTEROSAURIA CHAP. 



there are many others. Ophthalmosaurus, of the Upper Oolitic and 

 Cretaceous formations of England, had very small vestigial teeth. 

 Baptanodon, of the Upper Jurassic epoch of Wyoming, was 

 toothless, and was one of the six-toed forms. 



SUB-CLASS IX. PTEROSAURIA. 



Mesozoic reptiles with fixed quadrate bones and with the anterior 

 limbs transformed into wings, the enormously elongated ulnar 

 finger carrying a patagium. 



The skull bears a superficial resemblance to that of Birds. 

 It articulates with the neck by a single condyle, at nearly a right 

 angle. The interparietal foramen is absent, but there are five 

 pairs of foramina on the surface of the skull, namely, the nostrils, 

 orbits, supra- and infra-temporal and pre-orbital foramina. Most 

 of the constituent bones of the cranium fuse with each other, and 

 the composition of the various arches is therefore difficult to 

 make out with certainty. The premaxillaries are fused together, and 

 extend dorsally backwards between the nasals, which themselves 

 diverge towards the prefrontals. The nostrils are bordered 

 chiefly by the maxillaries, nasals, and prefrontals. The orbits 

 are very large, mostly shut off in front from the pre-orbital 

 foramina by a bridge, which is formed by descending processes 

 of the prefrontals and ascending processes of the jugal. Above 

 and behind, the orbits are bordered by the frontals, postfrontals, 

 and possibly the quadrato-jugals. The whole temporal region is 

 shortened from before backwards, but heightened dorso-ventrally, 

 and the whole temporal fossa is divided into a supra- and infra- 

 temporal portion by the junction of the postfrontal with the 

 squamosal, the latter joining the parietal, thus closing the supra- 

 temporal fossa behind. This is conspicuous only in the older 

 forms, e.g. Dimorphodon, but is very small in Pterodactyl us, and 

 quite abolished in Pteranodon. The infratemporal fossa is a 

 narrow slit, slanting obliqujely upwards and backwards, between the 

 quadrate and the quadrato-jugal. A foramen of this kind occurs 

 elsewhere only in the Rhynchocephalia. The quadrate is long, 

 firmly fixed, and slants so far forwards that the mandibular joint 

 lies on a level below the middle of the orbit. The pterygoids 

 articulate with strong and long processes of the basisphenoid, 

 touch the quadrate posteriorly, enclose an interpterygoid vacuity, 



