178 FLYING SAURIANS. 



use of this disposition of tiie shortest joints in the middle of 

 the toes of Lizards, is to give greater power of flexion for 

 bending round, and laying fast hold on twigs and branches 

 of trees of various dimensions, or on inequalities of the sur- 

 face of the ground or rocks, in the act of climbing, or run- 

 ning.* 



All these coincidences of number and proportion, can 

 only have originated in a premeditated adaptation of each 

 part to its peculiar office ; they teach us to arrange an ex- 

 tinct animal under an existing family of reptiles ; and when 

 we find so many other peculiarities of this tribe in almost 

 every bone of the skeleton of the Pterodactyle, with such 

 modifications, and such only as were necessary to fit it for 

 the purposes of flight, we perceive unity of design per- 

 vading every part, and adapting to motion in the air, organs 

 which in other genera are calculated for progression on the 

 ground, or in the water. 



If we compare the foot of the Pterodactyle with that of 

 the Bat, (see PI. 22, k,) we shall find that the Bat, like most 

 other mammalia, has three joints in every toe, excepting 

 the first, which has only two ; still these two, in the Bat, are 

 equal in length to the three bones of the other toes, so that 

 the five claws of its foot range in one strait line, forming- 

 altogether the compound hook, by which the animal sus- 

 pends itself in caves, with its head downwards, during its 

 long periods of hybernation ; the weight of its body being, 

 by this contrivance, equally divided between each of the ten 

 toes. The unequal length of the toes -of the Pterodactyle 

 must have rendered it almost impossible for its claws to 

 range uniformly in line, like those of the Bat, and as no 

 single claw could have supported for a long time the weight 



same reasons that are assigned respecting the number of joints in the fiftli 

 finger. In the P. Longirostris, Cuvier considers the small bone, (PI. 21, 5, 

 6,) to be a rudimentary form of the fifth toe. 



* A sirnilur numerical disposition prevails also in the toes of birds, at. 

 tended by similar advantages. 



