276 VERTEBRATE ANIMALS. 



genuine reptiles. The only living Reptile which has any power of sustaining 

 itself in the air is the Flying Dragon (Draco), which has been previously men- 

 tioned. In this case, however, the animal has no power of true flight, hut is 

 simply enaliled to take extensive leaps liy means of a membranous expansion 

 on each side of the body. In the Bats, again, the power of genuine flight is 

 present ; and this given by means of a leathery membrane which is supported 

 chiefly by certain of the fingers— which are greatly lengthened— and is attached 

 to the sides of the body and hind-limbs. 



In the Pterodactyles the power of true flight was present ; and this was also 

 conditioned by means of a leathery expanded membrane, attached to the hind- 

 limbs, the sides of the body, and the fore-limbs. In this case, however, the 

 chief support of the flying membrane was deriveil from the outermost finger 

 of the foredimb, which was enormously elongated (fig. 200). That the Ptero- 



Fig. 200. — Pk rod'iftiiluscrassirostrig. From tlie Lithographic Slates of Solenhofen (Upper 

 Oolite). In ;ircordance with tlie view nri;,dnal]y entertained, the digits of the hand 

 are liere erroneously rejiresented as ftVLi instead of four in number. 



dactyles passed their existence chiefly in the air, and did not simply leap from 

 tree to tree, is sliown by two characters in which they agree witli the flying 

 birds. Many of the bones, namely, were "pneumatic " — that is to say, were 

 hollow, and were filled with air. Secondly, whilst the shoulder-girdle has 

 many of the characters of that of birds, the breast - bone {stermim) is fur- 

 nished with a prominent ridge or keel, serving for the attachment of the great 

 muscles which work the wings. Tliere can be no doubt, therefore, as to the 

 Pterodactyles having enjoyed the power of genuine flight. Many of them 

 attained no great size, but some of theiu must have been gigantic, the expanse 

 of wing in one species having been calculated at probably about twenty-seven 

 feet from tip to tip. 



