So diverse are the functions of the fore limb in Dinosaurs and Pterodactyles, and so remarkably does the length of the metacarpal region of the back of the hand vary in the long-tailed and short-tailed Ornithosaurs, that there is necessarily a less close correspondence in that region of the skeleton between these two groups of animals; for the Pterodactyle fore limb is modified in relation to a function which can only be paralleled among Birds and Bats; and yet neither of those groups of animals approximates closely in this region of the skeleton to the Flying Reptile. Under all the modifications of structure which may be attributed to differences of function, some resemblance to Dinosaurs may be detected, which is best evident in the upper arm bone, humerus; is slight in the fore-arm bones, ulna and radius; and becomes lost towards the extremity of the limb. If the tendency of the thigh bone to resemble a Mammalian type of femur (p. 100) is a fundamental, deep-seated character of the skeleton, it might be anticipated that a trace of Mammalian character would also be found in the humerus. For what the character is worth, the head of the humerus does show a closer approximation to a Monotreme Mammal than is seen in Birds, and is to some extent paralleled in those South African reptiles which approximate to Mammals most closely. Not the least remarkable of the many astonishing resemblances of these light aerial creatures to the more heavy bodied Dinosaurs is the circumstance that the humerus in both groups makes a not dissimilar approach to that of certain Mammals.