80 
FOSSIL REPTILIA OF THE 
the two bones. In the Bird incapable of flight the humerus is solid ; 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 pneumaticity 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, difference 
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 cliffs 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 representative of the order. 
Ramphorhyncims Meyeri, PI. XIX, fig. 5. — In further illustration of the characters 
of Divwrphodon 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 Ramphorhyncims Gemniingi, V. M.^ 
1 See Von Meyer, op. cit., pi. i.x, fig. 1. 
