use of this disposition 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 dimensions, or on inequalities of the surface of the ground or rocks, in the act of climbing, or running.[1]
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 extinct 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 pervading 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 Pl. 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 suspends
itself in caves, with its head downwards, during its
long periods of hibernation; 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 fifth finger. In the P. Longirostris, Cuvier considers the small bone, (Pl. 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.
