9i MR. H. Q. SEELET ON THE 



ber of vertebrae in the several regions of the body is not easily 

 determined. There appear to be usually seven or eight cervical 

 vertebrae, vsrliich is fewer than is recorded in any bird, though the 

 number is not more reptilian than mammalian. Sometimes the ver- 

 tebrae are elongated, subcylindrical, and without conspicuous pro- 

 cesses, as in Pterodactylus longirostris, and then tbey closely re- 

 semble in form the vertebrae in the neck of the Purple Heron. 

 If there were any ground for comparing the animal, as a whole, 

 witb Terrapins, a certain parallelism would be remarked in the 

 form of the neck-vertebrae of the two groups. 



In other genera of Ornitbosaurs from the litbographic slate, 

 such as Cycnorhamphus, in Dimorphodon from the Lias, and in all 

 the Ornithocheiroidea from the Cretaceous strata, tbe neck-ver- 

 tebrae are large, broad from side to side, more or less flattened on 

 the under face, and have the neural arch extending transversely 

 beyond the ceutrum, as in Bucorvus abyssinicus. But birds, even 

 raptorial birds, have a much smaller development of the neural 

 spine. No reptile has a neck formed on this plan. 



As yet, the nature of the articulation of the centrum in the ver- 

 tebrae of most Ornithosaurs from the lithographic slate is unknown, 

 though the condition is certainly not uniform. In the genera 

 from the Cambridge Upper Greensand and the Chalk all the ver- 

 tebrse have the centrum depressed ovately, concave in front, and 

 convex behind. Some of the vertebrae of Dimorphodon have the 

 same character. But the elongated caudal vertebrae of that genus, 

 like similar vertebrae from the Oxford and Kirameridge Clays, have 

 the articular ends of each centrum biconcave, as are the later 

 caudal vertebrae in most Vertebrata. This proccelous character 

 of the neck and back is at once a difference from all known birds, 

 and a resemblance to the form of vertebral articulation among 

 lizards, serpents, and crocodiles. The resemblance is the more 

 worthy of being carefully weighed, because no mammals are re- 

 ported to possess proccelous vertebrae. Although, no doubt, a 

 biconcave vertebra, such as that of IchtTiyornis, or of the tail of 

 an existing bird, might become as easily moulded to the lacertilian 

 as to the avian form, hitherto the condition has not occurred in 

 birds, recent or fossil ; but on that account the probability of its 

 occurrence hereafter is not decreased. 



Nevertheless the character can scarcely be called reptilian, 

 since in such reptiles as the Chelouians and Ehynchocephala for 

 example other modes of vertebral articulation prevail. If the 



