Order EODENTIA. 



This is a large group contaihing the so-called "gnawing " 

 animals, which are usually of small size and are 

 characterized by the possession of chisel-like incisor teeth 

 in both jaws, which are curved, rootless and extend far 

 back into the jaws : these teeth grow throughout the 

 life of the animal and are kept within bounds by the 

 gnawing of wood, &c. There are no canine teeth, and 

 the premolars are reduced. Their feet are plantigrade or 

 nearly so. Eodents are found all over the world, being 

 commonest in South America, and scarcest in Madagascar 

 and Australia. Most rodents are herbivorous, although 

 some are carnivorous feeders. Typical rodents first made 

 their appearance in the Upper and Lower Eocene periods. 

 There are two sub-orders, the SimpUcidentata (with only 

 one pair of upper incisors) and the DupUcidentata (with 

 six above and two below at birth ; the outer pair of the 

 former is soon lost, the second pair being considerably 

 reduced in size, the third pair being large). The 

 Himplicidentata are divided into three "tribes": the 

 Hcmromorplia, containing the Squirrels and Beavers, the 

 Myomorpha, with the Rats, Mice, Jerboas, Mole-rats, &c., 

 and the Hystricomorpha containing the Springhares, 

 Porcupines, Agouties, Pacas, Cavies, &c. 



Family SCIUEIDiE. 



This is a small family in South Africa, containing only 

 four species of Squirrels. The skull possesses post-orbital 

 processes, and the molars are tubercular and rooted. The 

 premolars number two above and one below. 



