its first and second bones there was a marvelously perfect pulley-like joint, permitting the flexion of the finger through an arc of nearly one hundred and eighty degrees. When not in use in support of the wing membrane, the finger could have been folded back close to the arm, touching each other nearly on the back. In fact these bones have been found fossilized in this position.
Attached to the whole length of the arm and finger to its curved extremity, there was a thin, and certainly strong, membrane, which continued on the sides of the body and legs, probably quite to the rudimentary feet. Impressions of this membrane have been found, showing every fold and crease, as though cast in plaster-of-paris. Anterior Extremity of Wing of Pteranodon, Nine Feet in Length.
In size these highly specialized pterodactyls reached, as outspread in flight, the enormous expanse of more than nineteen feet from tip to tip of fingers. The length of the body from tip of bill to toes was about eight feet of which the head was nearly a half. Contemporaneous with these gigantic species were many others of smaller size, while related forms of an earlier period scarcely exceeded the stature of a common sparrow.
The earlier pterodactyls were smaller and in many other respects much less specialized than the latter ones, that is they departed less widely from the true reptilian type. Of these perhaps the best known is the Rhamphorhynchus, a restoration of which is given herewith, based upon a nearly complete skeleton in the Yale Museum, a specimen of great interest, because it shows so clearly the impressions of the wing membrane, wholly without hair, feathers or scales. In this pterodactyl, the jaws were provided with long and sharp teeth, the neck was less stout, the shoulders were loosely articulated, the bones of the wings less elongated, the legs stouter. Furthermore, it had a long, slender and flexible tail, provided at its extremity with a diamond shaped membranous expansion, which doubtless served as a steering organ or rudder in flight. Between the Rhamphorhynchus and Pteranodon there were many intermediate forms, both large and small, with and without teeth. Species of Ornithocheirus, nearly as large as those of Pteranodon, which they closely resembled, except in the presence