MAMMALIA. 557 
CHAPTER XXX, 
MAMMALIA —( Continued). 
Sub-Class III.—Eutheria. 
ORDER V.—Z£dentata. 
The general anatomical characters of the sloth have 
been already described, the animal being taken as a com- 
pletely arboreal type (page 533). The order appears to 
occupy the lowest place in the sub-class and its members 
have great diversity of habits. They are either arboreal 
and herbivorous or semi-fossorial and insect-eating. The 
body is clothed in hair, in one family supplemented by 
bony plates. Both pairs of limbs are well developed and 
armed with claws. The digits may vary from 2 to 5. 
The teeth are always either simple and homodont, with 
persistent pulps, and with few exceptions monophyodont 
or they are absent altogether. They are usually also 
deficient in enamel. and the incisors and canines always 
are absent. The order shows remarkable diversity in the 
structure of the placenta and in specialisations of teeth, 
limbs and body-covering. It is divided into two sub- 
orders which are widely separated, both structurally and 
geographically. 
SUB-ORDER I.—XENARTHRA. 
In this sub-order are contained at least four families. 
In them the uterus is simple and the placenta is dis- 
coidal or dome-shaped and deciduatee Mammez are 
usually two and pectoral. The vertebrae usually have 
