ICHTHYOSAURS 



other reptiles. They are the offspring of four- 

 legged terrestrial reptiles which have become 

 specially modified and adapted to submarine 

 life. Like many whales they had a median 

 fin on the back devoid of bony support. The 

 bones of their legs have become greatly changed, 

 much more so than those of the Plesiosaurs 

 and form often more than five rows of nearly 

 circular or polygonal plates fitted together as 

 a flexible paddle. The tail is fish-like, but has 

 the lower lobe bigger than the upper and the 

 vertebral column bends down into the lower 

 lobe instead of turning up into the upper lobe 

 as it does in fish. The details as to the fins are 

 known from some wonderfully preserved speci- 

 mens found in the fine hardened mud known as 

 the Hthographic slate of Solenhofen, where the 

 soft bodies of jelly-fish, cuttle-fishes and the 

 wings of flying reptiles also are preserved. 



As mentioned in the first chapter, the Ichthyo- 

 sauria (see Fig. 2) had a ring of bony plates 

 supporting the eye-ball (as birds also have), 

 and these are often preserved in the fossil 

 specimens. In Fig. 168 a view of the top of 

 the skull of an Ichthyosaurus is given in order 

 to show the round hole in the middle line of 



227 



