THE AI. 



166 



axilla. In quickly-moving animals this vessel reaches into the upper arm, and divides into a few 

 rather large ones lower down, and these give off others, so that a certain quantity of blood is supplied 

 and removed quickly. But in the Sloths the axillary artery divides at once into a number of 

 cylindrical vessels nearly 

 as large as it is, and they 

 are united here and there. 

 These unusual arteries are 

 found in contact with the 

 surface of the muscles, 

 and their branches go in 

 and amongst the muscular 

 bundles. As many as 

 forty-two of these iai'ge 

 vessels were counted by 

 Sir A. Carlisle, on the 

 surface of the muscles on 

 the front of the arm, and 

 probably about twenty 

 were inside. These arte- 

 ries thus carry an im- 

 mense supply of blood 

 to the muscles, but blood 

 which, although it is 

 finally removed by the 

 veins, does not move 

 very rapidly. In fact, 

 the muscles are turgid 

 with blood. The same 

 arterial structure is seen 

 in the hinder limbs, and 

 the arteries of the thigh 

 form as numerous a set 

 as those of the arm. 



It seems to be in 

 accordance with careful 



investigation, to State AI - ( From the Proceedings of the Zoological Society.) 



that the species of Sloth 



called Bradypus tridactylus (the Three-toed Sloth, or Ai) has too large a meaning, and that it really 

 refers to the Collared Sloth, as well as to others which have been placed in the next genus. It is as 

 well to remark here, that although there are three clawed fingers to the fore limb, there are vestiges 

 of two other ones by their side in the form of two rudimentary metacarpal bones. 



GENUS ARCTOPITHECUS. THE AT* 



Several kinds of three-clawed Sloths have been called Ai ; for instance, the Yellow-throated Ai, 

 and De Blainville's Ai, and all have been named Bradypus tridactylus. Dr. Gray, however, satisfied 

 himself that the kind which was first described by Cuvier as the Ai, and which is figured in 

 Prince Maximilian of Neuwied's " Animals of Brazil," is the same as one which has since been called 

 Arctopithecus Ai, or Arctopithecus flaccidus. The word Ai is taken from the noise made by the animal, 

 and the term flaccidus relates to its long hair. The true Ai inhabits Venezuela and Peru, and has 

 very long flaccid grey hair mottled with white. There is an abundant under-fur of a blackish brown 

 colour, which has white and black in spots and blotches. 



A rctopithecus flaccidus. Arctopithecus A i. 



116 



