230 FLYING SAURIANS. 
tion of the 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 di- 
mensions, or on inequalities of the surface of 
the ground or rocks, in the act of climbing, or 
running.* 
All these coincidences of number and pro- 
portion, can only have originated in a pre- 
meditated adaptation of each part to its pe- 
culiar office; they teach us to arrange an 
extinct animal under an existing family of rep- 
tiles ; and when we find so many other peculia- 
rities of this tribe in almost every bone of the 
skeleton of the Pterodactyle, with such modifi- 
cations, and such only as were necessary to fit 
it for the purposes of flight, we perceive unity 
of design pervading every part, and adapting to 
motion in the air, organs which in other genera 
we are considering, that it adds another approximation to the 
character of the living Lizards ; we have seen that it also 
differs from the other Pterodactyles, in having the fifth, instead 
of the fourth finger elongated, to become the expansor of the 
wing. 
It is however probable that the fifth toe had only three joints, 
for the same reasons that are assigned respecting the number 
of joints in the fifth finger. In the P. Longirostris, Cuvier 
considers the small bone, (PI. 21,5, 6,) to be a rudimentary- 
form of the fifth toe. 
* A similar numerical disposition prevails also in the toes of 
birds, attended by similar advantages. 
