CLASS MAMMALIA 



441 



and the presence of fatty humps containing a store of food which may 

 be drawn upon when they are forced to fast. Some of the ungulates 

 have the stomach divided into chambers and the cattle, which are 

 ruminants and chew their cud, have four chambers, known as rumen, 

 reticulum, psalterium, or omasum, and 

 ahomasum (Fig. 335). The food when 

 eaten is swallowed in the form of balls, 

 which are accumulated in the rumen. 

 Later, one by one, these are brought 

 back into the mouth, thoroughly masti- 

 cated, and swallowed again, passing 

 into the reticulum and on through the W 

 other chambers, being digested in the 

 meantime. 



The odd-toed ungulates, or Peris- 

 sodactyla (pe ris o dak' ti la; G., peris- 

 sos, odd, and dactylos, digit), include 

 those forms in which the middle digit 

 of both the fore- and hind limbs is 

 highly developed and carries most of 

 the body weight. Aside from the 

 horses the order includes tapirs and ^ , ^^| '• 



rhinoceroses. 



Proboscidea (pro b5 sid' e a; G., 



pro, in front, and hoskein, to feed) 



contains the elephants, which are the 



largest terrestrial mammals and which 



live to a great age, sometimes as much 



as two hundred years. The order Si- 



renia ( si re' ni a; G., seiren, a sea 



nymph) includes the manatees and 



dugongs, which are aquatic and herbiv- 

 orous animals with several character- in nature elsewhere. They have an 



, . , . , extremely long neck which enables them 



IstlCS betraymg a relationship to the ^o browse upon trees. Even though so 



elephants. The manatees are found in long, there are only seven vertebrae in 

 , „ . 1 ii J. c the neck, the normal mammalian num- 



the fresh waters along the coasts Ot ^er. (Photographed from a specimen in 



southern North America, northern the University of Nebraska State 



South America, and Africa; the du- 

 gongs inhabit Oriental and Australian waters. 



447. Cetacea. — In this section are the whalebone whales and the 

 toothed whales, the latter group including the sperm-whales, killer whales, 

 porpoises, and dolphins. They have a single or double median nostril 

 near the crown of the head and, when they rise to the surface, expire 

 forcibly, throwing a great column of steam into the air. This act is 



Fig. 339. — A male giraffe, Giraffa 

 reticulata. These ruminants live only 

 in Africa and apparently never existed 



