172 THE STORY OF REPTILE LIFE. 



of increased size, and in the development of 

 ornament, appear in the Pterodactyles of the 

 Cretaceous or Chalk age, some of the largest 

 of which attained a gigantic size, having an 

 expanse of wing of twenty feet, and a skull 

 a yard in length. Whilst some species were 

 tooth-bearing, others were entirely toothless. 

 But with or without teeth they must have been 

 formidable creatures flying-dragons, indeed ! 

 Animals of such enormous size, would, one 

 would have imagined, have become incapable 

 of flight, as in the case of the Ostrich-tribe 

 among birds. As a matter of fact, however, 

 the bodies of these flying monsters were remark- 

 able for their lightness, partly owing to the 

 extreme thinness of the bones, which were 

 almost paper-like in thickness. Furthermore, 

 the trunk, in proportion to the size of the head 

 and wings, was really extremely small. In one 

 genus at least, the bones of the shoulder-girdle 

 underwent a peculiar modification on account 

 of the great size of these wings ; inasmuch as 

 the shoulder-blade, instead of running backwards 

 parallel with the spine, and over the ribs, turned 

 directly inwards so as to lie parallel with the 

 ribs and at right angles to the spine with one 

 of the neural-arches of which it is articulated by 

 a special joint. This gave rigidity to the girdle. 

 Among the birds this very necessary stay is 

 provided by the merrythought, a bone con- 

 spicuous by its absence in the pterodactyle. 



The question of ornament is a delicate one, 

 inasmuch as this is for the most part an entirely 

 superficial character, and therefore leaves no 



