ICHTHYOSAURI A 



117 



resembling those of the fish-eating (l()li)hins. 'I1u'\ usualK- IkkI. 

 however, two attachments to the body of the vertebra and none to 

 the arch, chlTering in this respect from all other animals. 



Of the shoulder bones, the scapula or shoulder-blade, as usual 

 among water animals, is short and broad. In the place of a sternum 

 the coracoids joined each other broadly in the middle, just as they 

 did in the oldest known land reptiles. And there were clavicles 

 and an interclavicle. Below the abdomen behind were numerous 

 slender bones called ventral ribs. The pelvis is very weak, and 

 was suspended below the spinal column in the fleshy walls of the 

 abdomen. The hind legs were so small that little support was 



Fig. 55. — Pectoral girdle of Baplanodon {0 phthalmosaurus) , an .American Upper 

 Jurassic ichthyosaur. (After Gilmore.) 



necessary for them, and, because they were not used either for the 

 support of the body or for propulsion, they did not require a firm 

 union with the skeleton. Doubtless had the ichthyosaurs con- 

 tinued to the present time, they would have lost entirely the hind 

 legs, as have the cetaceans. 



It is in the limbs that most extraordinary differences from all 

 other animals are seen. So great are these dift'erences that it has 

 been a puzzle to naturalists to understand how they could have 

 arisen. In no other animals above the fishes, that is, in no other 

 reptiles, in no amphibians, birds, or mammals, are there ever more 

 than five fingers or five toes, the number with which air-breathing 

 animals began. Fingers and toes may be lost and often are lost 

 in all groups of life, until a single one in each limb may remain, as 

 in the domestic horse. An increase of fingers and toes, however, 

 seems to be an impossibility in evolution, and doubtless of real 



