MAMMALIA 45 S 



only digit, and the rhinoceros, which has the second and fourth, 

 as well. It is known that the remote ancestors of the horse had a 

 second and a fourth toe where only splints occur now, and even a 

 first and a fifth, where now there is no trace of either. The 

 horse has been domesticated as long as we have records and there 

 are approximately as many breeds of horses as of chickens, — 

 some half a hundred. The ass and zebra belong to the same 

 genus, — Equus. They both cross with the horse. Tapirs are 

 included in this order. 



Order Proboscidea (with proboscis). — Two living and many 

 extinct species of huge Placentalia with five digits, each with a 

 distinct hoof. The nose is much developed into a prehensile 

 organ, with corresponding changes in the skull for attachment of 

 muscles. The skin is thick and loose. The upper incisors grow 

 enormously, forming the tusks characteristic of the group. 

 There are no canines; molars are very complex. The two teats 

 are thoracic. The largest of the land mammals, the elephants 

 and the extinct mastodon and mammoth, belong here. They 

 are now confined to the tropical regions of Asia and Africa, 

 though in geological times they seem to have had a world-wide 

 range. The tusks of species of elephants, both living and 

 extinct, furnish the ivory of commerce. 



Order Carnivora (flesh-eaters). — The Carnivora are four- 

 or five-toed animals with the digits ending in claws. The 

 canines are well developed, strong and curved. The other teeth 

 are often pointed and adapted to holding or tearing. Muscles 

 of mastication are especially well developed. Mammae are 

 numerous, occurring along the entire abdomen. There are two 

 types of Carnivora — terrestrial and marine. To the first belong 

 the bear family, which is perhaps the least specialized group ; the • 

 dog family, including dogs, wolves, foxes, jackals ; the cat family, 

 including lions, tigers, leopards; hyenas; many fur-bearing ani- 

 mals — as otters, weasels, minks, martens, badgers, wolverines, 

 and skunks. There are many of these fur-bearing animals in 

 North America. The seals and walruses belong to the marine 

 group. In these forms the appendages have become adapted to 

 the water habit, the digits bearing intervening webs. 



The principal American cats are: the wild cat (also called 



