MAMMALIA 329 



Distribution, Cetacea are cosmopolitan, mostly marine. A 

 few ascend rivers, some being exclusively river forms of South 

 America and southeastern Asia. 



Use to Man. A good quality of ivory is obtained from nor- 

 whal's tusks (the left upper incisor which sometimes reaches a 

 length of 8 to 10 feet). Whalebone, oil, and spermaceti have 

 already been mentioned. 



Geologic Distribution. The cetaceans are represented in the 

 Eocene and Miocene of Europe, Egypt, and North America. 

 Both whalebone whales and toothed forms have been found in 

 the Pliocene deposits. The toothed whales are represented in 

 the Miocene, Pliocene, and Pleistocene of Europe, North Amer- 

 ica, New Zealand, and Australia by the extinct heterodont family 

 Squalodon' tidce . 



Order VI. Ungula'ta. This is a large order of diverse forms. 

 A large proportion of these forms are extinct, and existing forms 

 are connected to some extent by fossil forms. Many of these 

 animals are very large. They are chiefly herbivorous. The 

 molar teeth are adapted for grinding by having broad crowns, 

 with tuberculated or ridged surfaces. Canines are absent or 

 small, or, in a few cases, tusk-like in the upper jaw. Although 

 the older types were plantigrade, the existing forms, excepting 

 such as Hyrax, are digitigrade, walking on the tips of their 

 toes. The one-four terminal phalanges are nearly always en- 

 cased in solid horny hoofs, which are, in reality, enlarged and 

 thickened claws. The weight of the body usually rests upon 

 these hoofs. The limbs have no power of grasping or climbing, 

 but are simply organs of locomotion. Clavicles are absent. 

 This is the only order of mammals in which horns appear. They 

 are surely a needed and effective means of defense in those forms 

 which are too heavy to be swift, as they cannot defend themselves 

 with teeth nor claws, as do the rodents and carnivores. The 

 order contains many domesticated animals indispensable to man 

 as beasts of burden or as food. It is the most beneficial to man 

 of any order of mammals. 



The Hyrax (Hyracoi'dea). This and the following family are often 

 placed in a sub-order. They are the survivors of those great animals of 

 the past that had their wrist-bones placed in a longitudinal series and had 

 toes which were nearly equal in length. The hyrax (Fig. 268) is a small 



