112 STOEY OP THE EEPTILES 



put ribs the entire length, and in the back-bone she 

 put extra vertebrae (to the number of 300 in the 

 pythons) till the body was long and active. Each of 

 these joints she made of large balls and sockets, and 

 on the spines of the vertebrae she made other unusu- 

 ally large joining (articulating) surfaces in addition 

 to those already in the centers ; so that the back-bone 

 should not only be bent easily but stiffened quickly 

 and surely for good work. It is wonderful to see 

 what snakes can do with a back-bone only and a slight 

 movement of ribs and scales. They climb, leap, swim, 

 stand erect for half their length, and in a few cases 

 run swiftly. The author has seen the common gar- 

 ter-snake resting head downward on the rough bark 

 of a standing tree, the diameter of which was equal to 

 the length of the serpent ; and he has noted the com- 

 mon blacksnake, not four feet long, run, as fast as a 

 man would walk, through standing timothy two feet 

 high, holding its head well up above the grass. 



The movement of the tortoise-forms is often 

 merely a sliding one. Usually the breast is pushed 

 along by the claws. This is the case with many if 

 not all living lizards. But, while the slow progress 

 of the tortoise is proverbial, some of them can run 

 with the body clear of the ground and a few make 

 considerable speed in a dash for safety. 



Those turtles with paddles swim rapidly and cap- 

 ture fishes even by dashing at them or pursuing them. 



The running of some lizards is so rapid as to pro- 

 duce the effect of a mere streak, but it is not long 

 kept up. We have noted that one of the frilled \vl- 



