Closely connected with an animal's habits is the protection to the body which is afforded by the skin. In Pterodactyles the evidence of the condition of the skin is scanty, and mostly negative. Sometimes the dense, smooth texture of the jaw bones indicates a covering like the skin of a Lizard or the hinder part of the jaw of a Bird. Some jaws from the Cambridge Greensand have the bone channeled over its surface by minute blood vessels which have impressed themselves into the bone more easily than into its covering. Thus in the species of Ornithocheirus distinguished as _microdon_ the palate is absolutely smooth, while in the species named _machærorhynchus_ it is marked by parallel impressed vascular grooves which diverge from the median line. This condition clearly indicates a difference in the covering of the bone, and that in the latter species the covering had fewer blood vessels and more horny protection than in the other. The tissue may not have been of firmer consistence than in the palate of Mammals. The extremity of the beak is often as full of blood vessels as the jaw of a Turtle or Crocodile. COVERING OF THE BODY There is no trace even in specimens from the Solenhofen or Stonesfield Slate of any covering to the body. There are no specimens preserved like mummies, and although the substance of the wings is found there is no trace of fur or feathers, bones, or scales on the skin. The only example in which there is even an appearance suggesting feathers is in the beautiful Scaphognathus at Bonn, and upon portions of the wing membrane of that specimen are preserved a very few small short and apparently tubular bodies, which have a suggestive resemblance to the quills of small undeveloped feathers. Such evidences have been diligently sought for. Professor Marsh, after examining the wing membranes of his specimen of Rhamphorhynchus from Solenhofen, stated that the wings were partially folded and naturally contracted into folds, and that the surface of the tissue is marked by delicate striæ, which might easily be taken at first sight for a thin coating of hair. Closer investigation proved the markings to be minute wrinkles on the under surface of the wing membrane. This negative evidence has considerable value, because the Solenhofen Slate has preserved in the two known examples of the bird Archæopteryx beautiful details of the structure of the larger feathers concerned in flight. It has preserved many structures far more delicate. There is, therefore, reason for believing that if the skin had possessed any covering like one of those found in existing vertebrate animals, it could scarcely have escaped detection in the numerous undisturbed skeletons of Pterodactyles which have been examined.