THE VERTEBRATES 437 



3. Edentata (edentates) sloths, armadillos, most ant-eaters. 



4. Cetacea (cetaceans) whales, porpoises, dolphins. All are 



aquatic, with fish-like bodies, no posterior (pelvic) limbs. 



5. Sirenia the mantee or sea-cow. 



6. Ungulata (ungulates or hoofed mammals) horses, asses, 



zebras, tapirs, rhinoceroses, camels, cattle, sheep, goats, ante- 

 lopes, giraffes, deer, pigs, hippopotami, elephants, and extinct 

 mastodons. Numerous extinct ungulates are found as fossils. 



7. Carnivora (carnivors or flesh-eaters) cats, hyenas, dogs, 



wolves, foxes, jackals, bears, otters, weasels, seals, walruses. 



8. Rodentia (rodents or gnawers) rats and mice, rabbits and hares, 



squirrels, porcupines, and beavers. There are about 1500 

 species of rodents. 



9. Insectivora (insectivors) moles, shrews, and hedgehogs. 



10. Cheiroptera bats and flying-foxes. Several hundred species. 



11. Primates lemurs, marmosets, monkeys, baboons, gibbons, 



orangs, chimpanzees, gorilla. The highest family of this order 

 of mammals is the Hominidse, which includes only the human 

 species (Homo sapiens). See 369. 



361. Adaptations of Mammals. Space here will allow 

 only mention of some of the most remarkable cases of mam- 

 malian structures which are specially adapted. 



(1) Fore limbs of bats have been modified into wings for 

 flying, but still retain the same number and arrangement 

 of bones as in ordinary five-toed mammals. 



(2) Posterior limbs of whales have become rudimentary 

 in fitting to aquatic life. The remains of the bones are 

 often found several feet beneath the skin. Seals which live 

 partly on land make little use of their small hind legs. 



(3) The feet of most hoofed mammals show remarkable 

 adaptations. The typical foot originally had five toes, but 

 some of the toes have either become so small that they do 

 not touch the ground or have disappeared altogether. The 

 following examples will illustrate this point. An elephant's 

 foot has five complete toes (or digits) each with a hoof, and 

 all united by skin. The wild and domesticated hogs and 

 hippopotami have four toes on each foot, the first one (I) on 



