Page:Popular Science Monthly Volume 10.djvu/232

220 the creature specifically light in its flight. Like a bird, this creature has a largish breastbone, but from that point onward, so far as I can see, special, particular resemblances end, and a careful examination of the fore-limbs shows you that they are not birds' wings; they are something totally different from a bird's wings. And then, again (pointing to a chart), those are not a bird's posterior extremities, but are rather a reptilian's hind-limbs. The vertebræ present nothing that I need dwell upon, but the bones of the hand are very wonderful.

There are four fingers represented. These four fingers are large, and three of them—these, which answer to these three in my hands—are terminated by claws, while the fourth is enormously prolonged into a great jointed style. You see at once from what I have stated about a bird's wing that there could be nothing more unlike a bird's wing than this is. It was concluded by general reasoning that this finger was made to support a great web like a bat's wing. Specimens now exist showing that this was really the case, that this creature was devoid of feathers, but the fingers supported a vast web like a bat's wing, and there can be no doubt that this ancient reptile flew after the fashion of a bat. Thus, though the pterodactyl is a flying reptile, although it presents some points of similarity to birds, yet is it so different from them that I do not think that we have any right to regard it as one of the forms intermediate between the reptile and the bird. Such intermediate forms are to be found, however, by looking in a different direction. Through the whole series of mesozoic rocks there occur reptiles, some of which are of gigantic dimensions; in fact, they are reckoned among the largest of terrestrial animals. Some of them are forty and fifty, possibly more, feet long. Such are the Iguanodon, the Megalosaurus, and a number of others, with the names of which I will not trouble you. There are great diversities of structure among these great reptiles. Some of them resemble lizards in the proportions of their limbs, and have evidently walked on all-fours, in that respect resembling the existing crocodile; but in others you can trace a series of modifications in virtue of which the hind-limbs at length completely assumed the character of a bird's hind-limbs. I here indicate (pointing to a diagram) the hind limb of a crocodile, showing the bones of the hind-limbs and of the pelvis. These are the haunch-bones; these are the two leg-bones. Then comes the division of the foot which we call the tarsus, in which the component bones are separate and distinct from one another, from the bones of the leg and from those of the metatarsus. Then come the four toes, which alone exist in the hind-feet of the crocodile, and which are separate and distinct. The foot is flat on the ground, so that the legs spread out and the weight of the body hangs clumsily between them. Contrast this with what we find in the bird—the haunch-bone here is immensely elongated, and the joints of the