416 



METAZOAN PHYLA 



the nostrils directed downward, an opposable thumb and great toe, and a 

 shorter tail, which is nonprehensile and in many cases rudimentary. 

 Among the Old World monkeys are the baboons, mandrills, macaques, 

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



444. Ungulata. — The Artiodactyla (ar ti 6 dak' ti la; G., artios, even, 

 and dactylos, digit), or even-toed ungulates (Fig. 285), 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 life. The latter adaptation 

 involves particularly two features — the possession of cells connected 

 with the stomach in which they carry a reserve water supply, thus 



Psa/fer/'um 



Esophagus 



Abomasurt^ 



/?urrter7 



Fig. 286. — A ruminant stomach. The arrows show the direction of movement of the 

 food. The balls of cud pass down the esophagus and into the rumen; then into the reticu- 

 lum and back to the mouth; on the second swallowing the food enters a small passage in 

 the upper part of the reticulum formed by the apposition of folds, or valves, and is directed 

 into the psaltcrium. From several sources. 



enabling them to go for long periods of time without needing to secure 

 more; 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. 286). 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 masticated, and swallowed again, passing into the reticulum 

 and on through the other chambers, being digested in the meantime. 



The odd-toed ungulates, or Perissodactyla (pe ris o dak' ti la; G., 

 perissos, 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 weight (Fig. 285). Aside from the horses the order 

 includes tapirs and rhinoceroses. 



