FOSSIL VERTEBRATES—MAMMALIA 17 I 



enlargement of the muzzle ; the dentition was weaker in that 

 the incisors were lost entirely or in part, and the molars and pre- 

 molars were small and weak. The canines were greatly enlarged 

 and extended from the jaws as tusks that were protected by 

 a flange of the lower jaw. The top of the skull shows three 

 pairs of bony protuberances that were possibly the bases of 

 horns. The brain was little, if in advance, of that of the Cory- 

 photo?^ dae. 



Dinoceros {Unitatheriiini) . — Characters given in the descrip- 

 tion of the family. 



Artiodactyla. — The families that we shall consider are the 

 Antliracotlieridae ', the Siridae, the Oreodo?itidae, the Hippopotamidae , 

 the Camelidae , the Anoplotheridae ', the Tragididae, the Protoceratidae , 

 the Cervicoma, and the Cavicorna. 



A?ithracotlieridae . — This is an extinct family that is found 

 chiefly in the deposits of Europe and the East Indies. The 

 earliest member of the group occurs in the Eocene of Europe. 

 During the Miocene time it spread over the whole continent of 

 Europe and over North America. The whole group appears to 

 have died out in the Miocene. The animals were large, about 

 the size of the rhinoceros, and from that down to the size of a 

 pig. The head was long and low, with little development in the 

 cranial region and a consequently small development of the brain. 

 The teeth are of the low multitubercular type that is character- 

 istic of the pig family. The feet have four toes on each foot 

 and the metapodials of the middle pair are not united. 



A?ithracotherium, Oligocene, of Europe, England, and India, 

 and North America. 



Ancodus, Oligocene, of Europe, and North America. 



Merycopotamns, Pliocene, of India. 



Suidae. — This is a very large group that contains the existing 

 hog. There are many primitive characters in the group, such as 

 the complete dentition, and the generalized multituberculate 

 teeth. The limbs have either four or two toes and the metapo- 

 dials of the middle pair are not united. The living members of 

 the family are found in Asia, Africa, Europe, and America. 



