164 CHAPTERS ON EVOLUTION. 



their allies, that this curious reptile bears the closest resemblance ; 

 and a comparative glance at the hinder extremities of the crocodile, 

 bird, and its reptilian neighbour (Fig. 85), will suffice to show the 

 marked resemblances and gradation which connect, and at the same 

 time distinguish, this curious series of forms. The Compsognathus 

 limb stands intermediate betwixt the saurian (Fig. 85, c) and the 

 bird (A) ; and, strictly judged, is comparable most nearly to that of the 

 unborn chick. Those " dragons of the prime " known as Iguanodon 

 and Megalosaurus, from the Chalk and Oolite, are near relations of 

 Compsognathus. When we think of the size of these reptiles, which 

 attained a length of from forty to sixty feet, and of the probability 

 that, like their diminutive neighbour, they may have walked on two 

 legs, the origin of the giant footprints (Figs. 78 and 79) of the Triassic 

 Sand-stones would appear to present no special difficulties in the 

 way of satisfactory solution. 



Mention must here be made of the curious Pterodactyls (Fig. 86), 

 or those extinct reptiles of the Lias, Oolite, and Chalk, in which a wing- 

 membrane or fold of skin, similar to that seen in bats, stretched from an 

 outer and enormously elongated finger of each hand to the fore-limb, 



FIG. 86. SKELETON OF PTERODACTYL. (The wing membrane in black. 



sides of the body, and hind limbs, and between the hind limbs and 

 tail. By aid of this wing-membrane these literal " flying dragons " 

 must have winged their way through the air with ease and speed. 

 Their breast-bone was keeled like that of the bird (Fig. 76, /, g) ; their 

 shoulder-girdle was bird-like ; and their bones, as in birds, were hollow, 

 and were filled with air in place of marrow. The Pterodactyl brain 

 was essentially bird-like, but the hind limbs and pelvis were rep- 



