MAMMALIA 



265 



hundred barrels of oil and two tons of whalebone, The 

 toothed or sperm whales inhabit both the great oceans. 

 The dolphins occur in schools and 

 dart out and in the water at fre- 

 quent intervals. The common At- 

 lantic porpoise is the puffer seen 

 rolling in the breakers near the 

 shore. 



Hoofed Mammals (Ungulata). 

 The members of this order are nota- 

 ble for the variation in the number 

 of digits (toes or ringers) from one 

 to five. The horses are one-toed; 

 the cattle and deer, two-toed; the 

 pigs, four-toed; and the elephant, 

 five-toed. This condition is ex- 

 plained by the theory of evolution, 

 declaring that all ungulates origi- 

 nally had five digits to each limb, 

 but in some cases one or more has 

 been lost because they were not of 

 advantage to the species. The an- 

 cestors of the horse known by fossil 

 remains exhibit four complete toes, 

 and the most ancient mammals, liv- 

 ing several millions of years ago, all 

 had five toes on each limb. Rudi- 

 ments of these lost digits are present 

 in the horse, deer, and cow. The digits are numbered 

 from the inside outward, i.e., from the thumb toward the 

 little finger. The horse walks on the end of the third 



FIG. 301. Skeleton of a 

 liorsc that lived in Colo- 

 rado more than a million of 

 years ago. From Guide 

 Leaflet of the American 

 Museum by Matthews. 



