1 A statement has recently appeared in a semi–popular scientific magazine to the effect that the air of the present day could not support animals of such large span as the larger pterodactyls, and that consequently the barometric, pressure in Cretaceous times must have been about twice as great as it is now. But it may be doubted whether there is so great a difference between birds of the present day and pterodactyls in respect of span as the author of this theory believes. Pelicans reach a span of fifteen feet. Latham (“General History of Birds,” Vol. X., p. 48, 1824) gives records of the span of albatrosses of 10, n , 12, and 13 feet. He mentions the “Voyage from England to India in the year 1754,” by Ives (Edward), formerly Surgeon of Admiral Watson's ship and of His Majesty's Hospital in the East Indies, on p. 5 of which appears :—“An albatrose (sic), a sea fowl, was shot off the Cape of Good Hope, which measured 17J feet from wing to wing. A shark was also caught, and brought on board the Cumberland, with 72 young ones in her belly, each from 6 to 14 inches long.” A gentleman in India gave to one of us a detailed account of his shooting and measuring a bird, stated to be an adjutant, with a span of 18 feet. No reason can be given for believing that the largest existing birds would become incapable of flight were the earth to undergo a great reduction of atmospheric pressure. Large birds of heavy loading, such as the black vulture, can soar as well at a height of two miles above the earth's surface as at lower levels. At such a height the barometric pressure normally stands at about 20inches. There is reason for believing that pterodactyls were of much lighter loading than (he black vulture.

2 A restricted range of fore and aft movement could occur at the wrist joint, but, as will be shown later, this was so connected with movements of rotation as to be singularly ill adapted for purposes of progression.

3 G. F. Eaton, “Osteology of Pteranodon.” (Memoirs of the Connecticut Academy of Arts and Sciences, New Haven, Vol. II., July, 1910.)

4 “On the Skeleton of Ornithodesmus latidens, an Ornithosaur from the Wealden Shales of Atherfield (Isle of Wight).” (Quarterly Journal of the Geological Society, Vol. LXIX., June, 1913, No. 274, p. 372.

5 E. H. Hankin, “Animal Flight,” p. 156. (London : Iliffe & Sons, 1914.)

6 Imagine lines drawn along the greatest diameters of the facets at the two ends of the humerus. When seen in an end–on view of the humerus these two imaginary lines make an angle with each other, which we measured in two cases, and found to be 18° and 19° respectively.

7 The two terms, “distal,” meaning the side furthest from the body or from the centre of the object described, and “proximal,” meaning nearest the body, are in common use in anatomy, and might be found useful in other sciences

8 The small size of this bone—9.6 centimetres in a pterodactyl of 15 metres span—renders it unlikely that it supported a propatagium in the manner suggested by one of us. (“The Development of Animal Flight,” Aeronautical Journal, Vol. XVI., p. 28, January, 1912.) In the paper here quoted reasons are given (on aeronautical grounds) for believing that the earlier pterodactyls had four wings, of which the hinder pair were supported by the hind legs. Stromer has recently stated that one of his museum assistants recollects seeing a beautifully preserved specimen of the pterodactyl Rhamphorhyncus in the shop of a dealer some ten years ago, and that this specimen showed a wing membrane supported by the hind leg and passing from the fifth toe of the hind foot to about half way along the tail. This statement appears to deserve further investigation, and if the specimen is still in existence, it would be of great interest for it to be examined and described. Stromer states that the tail fin of Rhamphorhyncus was horizontal, and not vertical, as has hitherto been supposed to be the case. Thus the only instance that has been adduced of the use of a vertical fir. by a flying animal turns out to be a myth. (Ernst Stromer, “Bemeikungen zur Rekonstruktion eines Flugsaurier–Skelettes,” Zeitschrift der Deutschen Geologischen Gesellschatt, Vol. 62, 1910, Berlin, footnote on p. 88.)

9 The albatross and certain other of the larger soaring birds resemble pterodactyls more than do other birds in the lightness of the structure of their wing bones. It is probable that the wing membrane of the larger pterodactyls was attached to the hind legs. Hence the pull from this membrane must have tended to draw the legs apart. The muscles that could have opposed this tendency must have been weak, judging from the curiously small size of the pelvis. This weakness of the muscles suggests that the wing membrane was extended across from one hind leg to the other, an arrangement that would diminish the work required from the leg muscles. An analogy for such an arrangement for the hinder part of the volant membrane is given by the vampire bats where there is an interfemoral membrane in the absence of a tail capable of aiding in its support.

10 “Animal Flight,” p. 121.