Quite in the type of the Saurians are the abdominal ribs, which are wanting to all birds and mammals, but often occur in the Lacertian order. The structure of the shoulder and breast-bone separate the Pterodactyle from the mammal, these parts being formed after the type of the Birds and Saurians, the characters of which are blended together. The small and elongated shoulder-blade, like the coracoid bone, belongs to the type of the bird rather than to that of the Saurians, of which, in reference to the last-named bone, only crocodiles have a similar one. The breast-bone, by its large expansion, points to the crocodiles, but at the same time, by the want of the keel, points to the ostrich-like birds, save that it is proportionally larger and wider than in these. The Pterodactyle, in common with the crocodile, wants the patella. The pelvis is formed on the type of the Saurians, although the ilium, by length and form, points somewhat to the mammals. The length and delicate form of the long bones of the limb, as well as the larger development of the fore-arm than of the upper-arm, and larger development of the lower thigh than of the upper thigh, and the thinness and elegance and shortness of the ?fibula (Wadenbein) have the characters of birds. The length of the middle hand [metacarpals] resembles that of birds, but its form in Pterodactyle is conformable to that of mammals. The first three fingers have the form and condition of the phalanges of lizards. The phalanges form the series 2, 3, and 4. The fourth, or air-finger, on the contrary, is of a peculiar type, of which no analogue is found in other animals, unless a somewhat similar arrangement be accredited to the bats. It is of enormous length, composed of four parts and without a claw. The hind-leg is, in proportion to the fore-leg, weak, and in general does not take the bird-form, but that of a Saurian. It has five toes, with unusual arrangement of the phalanges into the series 1, 5, 4, 3, 2. One toe has no nail, and the others have claws weaker than those of the hand. It can hardly be supposed that the animal lived in the water. All Saurians that live either in the water or on land are short-legged; it is the same with the swimming birds. But the Pterodactyle has its hind-legs as long as a land or air-bird; and as in these, the shin especially exceeds the length of the thigh. At the same time the toes, when they are in their natural position, were so close together that we may suppose the animal not to have been web-footed. The great development of the hand, by means of the long middle hand and especially of the enormous length of the air-finger, makes it probable that it was the chief organ of flight, as in birds and bats; also deviating in a peculiar manner from both these types, the long air-finger served to expand the wing-membrane, which extended from the upper part of the finger to the trunk, and which in all probability did not touch the hind-legs.