1392 THE STORY OF THE UNIVERSE 



Sauria: they are always articulated to the extrem- 

 ities of the transverse processes of the vertebrae, of 

 which they appear to be continuations. Processes 

 of this description also occur in the neck, attached 

 to the transverse processes of the cervical vertebrae; 

 and these have been regarded as cervical ribs. Their 

 presence are impediments to the flexions of the neck; 

 whence arises the difficulty which the crocodile ap- 

 pears to have in bending the neck, while turning 

 round upon the animal he is pursuing. In the 

 thorax, the ribs are connected with a broad sternum; 

 but there are other ribs, both before and behind, 

 which have no such termination, and therefore bear 

 the name of false ribs. 



The toes are usually provided with membranes 

 spread between them, to assist in swimming. The 

 form of the tail, which is generally compressed ver- 

 tically, like that of fishes, though perhaps not to an 

 equal degree, is another indication of their being 

 formed for an aquatic life: for where the tail has this 

 shape, we always find that the chief muscular power 

 is bestowed upon it as an instrument of aquatic 

 progression, producing, by its lateral flexions, a hori- 

 zontal movement of the body. Crocodiles and alli- 

 gators, for instance, which have this conformation, 

 are comparatively weak when on land, and as soon 

 as they have seized their prey their efforts are al- 

 ways directed to drag it with them into the water; 

 knowing that when in their own element they can 

 readily master its struggles, and dispose of it as they 

 please. 



In the Gecko tribe we find a particular mechanism 



