80 



FOSSIL REPTILIA OF THE 



tlie two bones. In the Bird incapable of flight the humerus is soHd ; in the Bird remark- 

 able for the long-continued power of soaring in upper regions of the air the shaft of the 

 bone is a ' thin shell of compact osseous tissue.' The relation of the weight of the volume 

 of air occupying the capacious cavity of the Argala's wing-bone to the total weight of 

 its body need not be taken into account in considering the problem of flight, but the 

 relation of a hollow instead of a solid humerus is a legitimate element in the endeavour 

 to solve that complex kind of animal locomotion. To say that a certain amount of weight 

 in the bird is essential to the momentum of flight is no argument against the reduction 

 to such requisite weight of the body to be upborne. Every structure so tending to 

 lighten the body of a volant animal within the required limit is, and ought to be, recog- 

 nisable as physiologically related to flight. 



By the pneuniaticity of the bones of the Pterodactyle, it might be inferred, from a 

 single bone or portion of bone, to have been an animal of flight. For, although certain 

 volant Vertebrates, e. g. the Bat and the Swift, may not have air-bones, no Vertebrate save 

 a volant kind has air admitted into the limb-bones. But the effect of such admission, 

 of such substitution of a lighter for a heavier material, is to diminish the weight without 

 impairing the strength of the bone ; the legitimate, if not sole, inference, therefore, is 

 that it contributes to perfect the mechanism of flight. 



It is a purely adaptive character, and the insignificant, barely appreciable, difierence 

 of weight due to difference of temperature in a given bulk of air makes the pneumaticity 

 of the skeleton as available and advantageous to a cold-blooded as to a warm-blooded 

 volant Vertebrate. 



In concluding the description of the subjects of the present Monograph I am moved 

 again to express my sense of acknowledgment for the most instructive of the evidences 

 of Dimorphodon macronyx due to my friend from the beginning of our palaeontological 

 pursuits, the Earl of Enniskillen, F.R.S. ; and, whilst fulfilling this pleasurable duty, I 

 would add a testimony to one whose loss Palaeontology has much reason to deplore, — to 

 the unwearied and undaunted explorations of the precipitous chfis of Lyme-Regis by 

 Mary Anning, to which, and to her singular tact of discernment of the feeblest evidence 

 of a fossil in that dark matrix, science is indebted for the discovery of the first evidence 

 of a Pterosaur in ' Lias ' of the locality, which has since yielded the grounds for the 

 reconstruction of the strangest reprcsentativ^e of the order. 



Rawphorhynclim Mcyeri, PI. XIX, fig. 5. — In further illustration of the characters 

 of Dimorphodon macronyx I have added to PI. XIX a figure of a long-tailed Pterosaur 

 from the lithographic slate of Pappenheim, which, in the feebleness of its hind-limbs and 

 the general proportions of the tail, resembles Ramphorhynchus Gemminyi, V. M.^ 



1 See Vol) Meyer, op. cit., pi. ix, fig. 1 . 



