LIFE AND KINSHIP OF DINOSAURS. 619 



Birds ? Do we get an explanation of the small fore-limbs by the picture which Professor 

 Phillips, under Huxleyan guidance, vividly presents to us " of the grand and free march 

 on land chiefly, if not solely, on the hind-limbs ?" Or, is the fact of the disproportion of 

 size between the arms and legs in the Megalosaur and Iguanodon susceptible of 

 other than the Oxfordian hypothesis ? 



As a matter of fact, such disproportion is shown by Crocodilian Reptiles still in 

 existence ; whilst extinct Crocodiles of more aquatic habits and marine sphere of life had 

 the fore-limbs as much reduced in size as in any known Dinosaiu'.* Of this Teleosaurian 

 character the physiological explanation which has been advanced is, that the com-se of 

 such Crocodile through water, due to the action of the long, laterally flattened tail, would 

 be facilitated, or less impeded, by such reduction of size of the fore-Hmbs ; those limbs 

 taking no share in the forward dash of the piscivorous reptile in pursuit of its prey, and, 

 if of any use in the water, being limited in natatory evolutions to assist in a change of 

 direction ; the fore-limbs, in fact, being mainly if not wholly required to help in the progress 

 of the amphibious beast upon dry land, or to scratch out the nest in the sand. Actual obser- 

 vation of a swimming Crocodile or Lizard testifies to the fore-limbs being then laid flat 

 and motionless upon the sides of the chest. All known Dinosaurs have the Crocodilian 

 swimming organ ; the Iguanodon exemplifies the compressed vertically broadened tail in 

 an eminent degree. And just as such appendage was essential to the proportion of the 

 active life of these huge cold-blooded amphibians which was spent in the watery element, 

 so such far-produced caudal fin must have been a cumbrous impediment to the way of 

 walking upon dry land pictured in the Work and Paper above cited.f 



In the ratio in which the fore-limbs approach the hind ones in size may be inferred 

 the proportion of time spent by the huge reptile on land, and the importance of the share 

 taken by these Hmbs in such quadrupedal mode of progression : when the Dinosaur 

 betook itself to water its fore-limbs would be, most probably, disposed as in the 

 Crocodiles. 



If, then, the hypothesis that the reduced fore-limbs of Dinosauria receive the most 

 intelligible, and therefore acceptable, explanation, admitting the principle of adaptation of 

 structures to functions and reciprocally, agreeably with the analogy of such living animals 

 as are most nearly allied to them in organization ; the notion that Birds, under their 

 wingless conditions, were derived from Dinosaurs may be safely left to the judgment of 

 whomsoever may be disposed to bring unprepossessed and impartial judgment to the 

 consideration of the hypothesis. 



* ' Crocodilia,' Plate 1, of the present "Work, and "Monograph on the Fossil Reptilia of the London 

 Clay," part ii, in the Volume of the Palreontographical Society for 1849, p. 24, t. xi. 



t Phillips, ' Geol. of Oxford,' p. 19G; and Huxley, ' Quarterly Journal of the Geological Society,' 



16^ 



