TEETBBRATA. 245 



Tolypeutes. Megatheriida. Bradypodid(s(Slot,hs}. 



Da 8 ypus(Armadillo). * Meg alonyx. Bradypus=Acheus. 



, ., .., ^Megatherium. Cholopus. 



Glyptodontida. * Mv f odon 



*Glyptodon. *Sphenodon. 



Order IV. EODENTIA. 



GLIRES. EOSORES. 



Two long, incurved incisors in each jaw, remote from the 

 molars ; no canines. Hallux not opposable to the digits. Cla- 

 vicles generally present. 



The molar teeth are few in number, and are transversely pene- 

 trated by the enamel ; they have often no roots, or the roots are 

 tardily prod uced. The incisors, separated by a wide interval from 

 the molars, are bevelled off 1 on the inner surface from attrition ; 

 but they continue to grow from the base through life, and thus 

 they preserve a uniform length. In early life in hares and 

 rabbits there are six upper incisors, but four of them are deci- 

 duous. There are, however, in the adult two supplementary 

 teeth behind the upper ones. The upper lip is sometimes di- 

 vided. The fore feet are frequently used as hands ; the hind 

 feet in a few species, like the jerboa, are of great length, chiefly 

 owing to the extreme development of the metatarsal bone. The 

 mammae vary from two to ten, and are pectoro-abdominal or 

 entirely abdominal. The stomach is simple ; the caecum is of 

 large size, but is absent in the dormice, and the intestines are very 

 long. 



Some of the Eodentia build nests ; they are very prolific ; 

 many, especially in northern climates, hibernate. In a few of 

 those that lead a subterranean life the eyes are reduced to a small 

 bulb. The brain is smooth and without convolutions. The orbits 

 are incomplete, not being separated from the temporal fossae. 

 Clavicles may or may not be present. 



The greater part of the Eodentia feed on vegetable matter of 

 one kind or another, but some are omnivorous. About 700 spe- 

 cies are known, 100 of these are found in Europe. 



Among the members of this order are, the hare (Lepus timidus), 

 rabbit (Lepus cuniculus), chinchilla (Chinchilla lanigera), guinea- 

 pig ( Cavia aperea), porcupine (Rystrix cristata), lemming (My odes 

 lemmus), black rat (Mus rattus), the brown rat, introduced, and 

 now the commonest of the two (Mus decumanus), mouse (Mus 

 musculus), harvest-mouse (Mus messorius), wood-mouse (Mus syl- 



