FIG. 32. THE PELVIC BONES OF AN ALLIGATOR SEEN FROM BELOW
The bones in front are here regarded as prepubic, but are commonly named pubic
This median union of the prepubic bones is a difference from those mammals like the Ornithorhynchus and Echidna, which approach nearest to the Reptilia. In them the prepubic bones have a long attachment to the front margin of the pubis, and extend their points forward without any tendency for the anterior extremities to approximate or unite. The marsupial mammals have the same character, keeping the marsupial bones completely distinct from each other at their free extremities. The only existing animals in which an approximation is found to the prepubic bones in Pterodactyles are Crocodiles, in bones which most writers term the pubic bones. This resemblance, without showing any strong affinity with the Crocodilia, indicates that Crocodiles have more in common with the fossil flying animals than any other group of existing reptiles; for other reptiles all want prepubic bones, or bones in front of the pubic region.
THE HIND LIMB
The hind limb is exceptionally long in proportion to the back. This is conspicuous in the skeletons of the short-tailed Pterodactyles, and is also seen in Dimorphodon. In Rhamphorhynchus the hind limb is relatively much shorter, so that the animal, when on all fours, may have had an appearance not unlike a Bat in similar position. The limb is exceptionally short in the little Ptenodracon brevirostris. The bones of the hind limb are exceptionally interesting. One remarkable feature common to all the specimens is the great elongation of the shin bones relatively to the thigh bones. The femur is sometimes little more than half the length of the tibia, and always shorter than that bone. The proportions are those of mammals and birds. Some mammals have the leg shorter than the thigh, but mammals and birds alone, among existing animals, have the proportions which characterise Pterodactyles. The foot appears to have been applied to the ground not always as in a bird, but more often in the manner of reptiles, or mammals in which the digits terminate in claws.
THE FEMUR
On the right is a front view of femur of a bear. In the middle are front and side views of the femur of Ornithocheirus. On the left is the femur of Echidna. These comparisons illustrate the mammalian characters of the Pterodactyle thigh bone