166 NATURAL HISTORY. 



There is a small spot between the shoulders on the back, where the fur is soft and woolly, and a 

 broad, short, blackish streak there, with a white or orange ring around it. The claws are coloured 

 brown. The head has a curiously-cut short and turned-up nose appearance, and is furnished with 

 coarse shaggy hair, disposed on the crown in a diverging manner. The short hair of the face contrasts 

 with the long, shaggy, shrivelled, dry, hay-looking hair of the body. This hair is coarse and flattened 



at the ends, but it is exceptionally fine at the roots* 

 and it greatly resembles in colour and texture some 

 of the vegetation of the trees on which it lives. The 

 eyes are bright, and are surrounded by a dark ring. 

 Several species of the genus Arctopithecus have been 

 described which live in Guiana, Bolivia, Brazil, Peru, 

 and Venezuela. 



The next genus of the Sloths is represented by 



THE TWO-FINGERED SLOTH (THE TJNAU).* 



There are several kinds of Sloths with two 

 " toes," or rather with two fingers ending in claws 

 SKVLL OF AI. on the fore limb, but the differences between the 



species are not very readily appreciated. They are 



differences which can be recognised, but it is doubtful whether the possession of dark brown or pale 

 brown hair is sufficient to decide that there are more than one species. 



The common Unau Sloth is usually of a darker tint than the others, but there is no doubt that 

 the specimens in museums of all these Sloths vary much in the colour and length of the hair. Thus 

 the hair may be generally dark, and the hairs of the crest on the back of the head may be white, and 

 more or less tinted with bright green ; or the hair may be short, of a dark brown colour, paler on the 

 rump, much paler on the head, cheeks, and chin ; a band may be across the nose, and the orbits dark 

 brown. Others of the same species have very long hair, of an uniform dark tint, paler 011 the head 

 and redder beneath, whilst one from Juan de Fuca has short hair, without any indication of a crest. 

 From Brazil there are specimens with long paler hair and a crest. All these specimens, however, 

 have pale whitish claws. 



A Unau from Columbia is of a pale and whitey-brown paper colour, darker at the root of the 

 hairs, and it has pale fawn-coloured claws. 



In all these animals with different kinds of furs, the two-clawed condition is peculiar to the fore 

 limbs only, for on the hinder there are three claws, and it is to be remarked that the hair and skin unite 

 the fingers and toes close up to the base of the claws. The skull of the Unau is rather projecting in front, 

 and not, as it were, quite cut off close ; and there is a great gap in. the upper and lower gums in front, 

 the incisor teeth being absent, of course. But at the side of the mouth there is a longish tooth above 

 and below, looking like a canine, but really it is the front molar, which in both jaws and on both sides 

 is longer and larger than the othei-s. The under teeth belonging to the lower molar set are placed 

 behind the corresponding upper ones when the mouth is shut. 



The cheek or malar bone is seen, on looking at the skull, to be separated from the ear bone, and 

 to have a forked end posteriorly, the lower part of the fork extending downwards and backwards. 



The lower jaw is very straight : it projects a little, in front and behind, where it is jointed with 

 the upper jaw, there is no upright portion or branch, or ascending ramus. The last back tooth is just 

 in front of a curved piece of bone called the coronoid process, the base of which is on a level with the 

 line of the teeth. 



This Sloth has seven neck bones (cervical vertebrfe), and the last one has a very small and 

 rudimentary rib attached to it on either side. There are no less than twenty-three dorsal vertebrae 

 found to be with ribs. The Unau has a clavicle which is much smaller in the other group. It has no 

 tail. The structure of the ankle joint enables it to turn in, oven more than that of the Three-clawed 

 Sloth. As the habits of the Unau Sloth are the same as those with three claws, and all live in the same 



* Cholcepus didactylus. 



