MAMMALIA. 557 



- CHAPTER XXX. 



MA MM A L I A —( Continued), 

 Sub-Class III.— Eutheria. 



Order V. — Edentata. 



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 deciduate. Mammae are 

 usually two and pectoral. The vertebrae usually have 



