502 BRITISH FOSSIL REPTILES. 



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

 of air occupying tlie 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 eff'ect 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. 



A specimen of the pterodactylian genus Bampliorhynchus, discovered in the litho- 

 graphic plate near Eichstiidt, Bavaria, with impressions of the wing-membranes, has been 

 obtained by Professor O. C. Marsh for the Museum of Yale College, New Haven, 

 United States. 



Of this rare specimen the accomplished Palaeontologist, by whom important additions 

 to Pterosaurian organisation had been previously made, has recorded a description in the 

 ' American Journal of Science,' vol. xxiii, with the subjoined figure of a restoration, in 

 which the condition of the specimen leads to a conclusion that the volant membrane, 

 after being continued from the hind-limbs upon the tail, is interrupted, and reappears as 

 a special terminal caudal expansion, or ' rudder,' as in the subjoined cut, on which is 

 .founded the specific name : — 



Ramphorhynchns phyl/urus, Marsh. 



