CRETACEOUS FORMATIONS. SI 



the species described above shall be designated Pterodactylus giganteus" (loc. cit., 

 p. 8.) Subsequent discoveries and observations have inclined the balance of pro- 

 bability in favour of the Pterodactylian nature of the fossils to which Mr. Bowerbank 

 refers. 



These fossils are not, indeed, amongst the characteristic parts of the flying reptile ; 

 one is the shaft of a long bone exhibiting those peculiarities of structure which are 

 common to birds and Pterodactyles ; the other shows an articular extremity which, in 

 our present ignorance of the different bones of the Pterodactyle, has its nearest 

 analogue in the distal trochlea of the bird's tibia. These two specimens, which are 

 figured in the above-cited volume of the ' Transactions of the Geological Society,' 

 PI. 39, figs. 1 and 2, were, in fact, as I acknowledged in the Memoir, read April 26th, 

 1840, transmitted to me by the Earl of Enniskillen and Dr. Buckland, as being the 

 bones of a bird (p. 411), and my comparisons of them were limited to that class. 



The idea of their possibly belonging to a Pterodactyle did occur to me, but it was 

 dispelled by the following considerations. The act of flight — the most energetic mode of 

 locomotion — demands a special modification of the vertebrate organisation, in that sub- 

 kingdom, for its exertion. But in the class Aves, in which every system is more or less 

 adapted and co-adjusted for this end, the laws of gravitation seem to forbid the suc- 

 cessful exercise of the volant powers in species beyond a certain bulk ; and when this 

 exceeds that of the Condor or Albatross, as, for example, in the Cassowary, the Emeu, 

 or the Ostrich, although the organisation is essentially that of the vertebrate animal 

 modified for flight, flight is impossible ; and its immediate instruments, to the exercise 

 of which all the rest of the system is more or less subordinated, are checked in their 

 development, and, being unfitted for flight, are not modified for any other use. There 

 is, perhaps, hardly a more anomalous or suggestive phenomenon in nature than a bird 

 which cannot fly ! A small section of the Mammalia is modified for flight ; but the 

 plan of the organisation of that warm-blooded class being less directly adapted for 

 flight than that of birds, the weight and bulk of the body, which may be raised and 

 transported through the air, are restricted to a lower range ; and the largest frugivo- 

 rous Bat (Pteropus) does not exceed the Raven in size. The Reptilian modification of 

 the vertebrate type would seem to be still less fitted for any special adjustment to 

 aerial locomotion ; and, in the present day, we know of no species of this class that 

 can sustain itself in the air which equals a sparrow in size ; this species, moreover, the . 

 little Draco volans, sails rather than flies, upborn by its outstretched costal parachute in 

 its oblique leaps from bough to bough. 



Of the remarkable Reptiles now extinct, which, like the Bats, had their anterior 

 members modified for plying a broad membranous wing, no species had been discovered 

 prior to 1840, which surpassed the largest of the Pterqpi, or "Flying-foxes," in the 

 spread of those wings, and there was a, priori a physiological improbability that the 

 cold-blooded organisation of a Reptile should, by any secondary modification, be made 



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