CLASS MAMMALIA 



439 



are distinguished by a broad nasal septum, a small nonopposable thumb, 

 and a long prehensile tail, which is used like a fifth hand. The Old 

 World monkeys, on the other hand, have a narrow nasal septum with 

 the nostrils directed downward, an opposable thumb, and a shorter 

 tail, which is nonprehensile and in many cases rudimentary. The great 

 toe is opposable in both New and Old World monkeys. Among the Old 

 World monkeys are the baboons, mandrills, macaques, and anthropoid 

 apes. Man is most closely related to the last-named. 



Fig. 336. — Musk ox, Ovibos moschatus (Zimmerman), of the Arctic barrens of North 

 America. The males secrete musk in the breeding season; hence, the name. They Hve in 

 herds, and at times of low temperatures or attacks by wolves they "huddle together" to 

 conserve their body heat or to protect themselves from the wolves. {Photographed from a 

 specimen in the University of Nebraska State Museum,.) 



446. Ungulata, — The Artiodactyla (ar ti o dak' ti la; G., artios, even, 

 and dadylos, digit), or even-toed ungulates (Fig. 330), include the swine, 

 hippopotamuses, camels, deer, antelopes, cattle, sheep, and goats. 

 They are animals with a hoof on each toe and are mostly two-toed, 

 although the hippopotamus has four toes. Many of these ungulates 

 are mud-loving and are restricted to the vicinity of water, while others, 

 like the camel, are adapted to desert Ufe. The latter adaptation involves 

 particularly two features — the possession of cells connected with the 

 stomach in which they carry a reserve water supply, thus enabling 

 them to go for long periods of time without needing to secure more; 



