172 SKETCH or THE HISTORY OF MAMMALIA. 



simple ; they are cylindrical, unrooted, consisting, as 

 Professor Owen has demonstrated, of a centre of vascular 

 dentine surrounded by unvascular dentine or ivory, the 

 whole enveloped by a layer of coementum, characterised 

 by numerous minute calciferous cells. Ill fitted for 

 grinding- the food, the teeth merely bruise it or break 

 down the tender structure of the buds or leaves, their 

 deficiency in this point being most probably compensated 

 by the singular complication of the stomach, which is 

 sacculated. 



The sloths bring forth and suckle their young like or- 

 dinary quadrupeds. They have two mammge, which are 

 situated on the breast ; and the young sloth, from the 

 moment of its birth, adheres to the body of its parent till 

 it acquires suflficient size and strength to shift for itself. 

 The head of the a'i is short, the face small and round 

 like that of the American monkeys, the ears concealed 

 in the long hair which surrounds them, the eyes small 

 and deeply sunk in the head, and the tail a mere rudi- 

 ment. The Indians like its flesh, and are in continual 

 pursuit of it. 



Naturalists reckon two distinct species of the ai, and 

 three or four varieties, some of which may probably be 

 found to be specifically different, when they come to be 

 dissected and carefully compared with one another. 1. 

 The Common Ai {Bradypus tridactylus^ Linn.) has a 

 short round head, furnished with coarse shaggy hair, 

 disposed on the crown in verging rays, like that of the 

 human species ; the face is of a yellowish colour, covered 

 with very short hair, whilst that of the body and extre- 

 mities is universally long and shaggy ; the eyes are en- 

 circled by a brown ring ; the hair of the body varied 

 with irregular patches of dark and light brown, or silvery 

 white : between the shoulders there is an oval patch of 

 short orange-coloured hair, of a finer quality than that 

 found on other parts of the body, and divided in the 

 centre by a longitudinal black stripe ; the throat and breast 

 are frequently of a light straw-colour. The texture of 

 the hair is altogether peculiar, and more nearly resembles 

 dry hay, or grass shrivelled and withered by the sun, 



