ioo Mr. Carlisle on a Peculiarity 



heart ? The extremely slow movements of the Bradypus tridac- 

 tylus are sufficiently known among natural historians. 



The Bradypus didactylus has its arterial system distributed in 

 some degree like the tridactylus ; but the brachial artery in the 

 upper limb is much less subdivided, as will appear by the repre- 

 sentation in Plate II. fig. 3; and, in the lower limb, the arteries of 

 the plexus afterwards divide a few times in the arborescent form. 

 It may be worthy of remark, that this correspondence of ar- 

 rangement, in the arteries of the lesser Sloth, bears a striking 

 analogy with the structure and habits of the large American 

 Sloth ; the movements of the Bradypus didactylus being univer- 

 sally represented quicker than those of the Bradypus tridactylus. 



The Lemur Loris was next examined, and its arterial system 

 was found to resemble those already described ; but, as the ani- 

 mal had been preserved in very strong spirit, the vessels were so 

 corrugated as not to admit of injection. The two Bradypi were 

 injected with quicksilver. The natural history of the Lemur Loris 

 appears not to be very well ascertained; but it is a slow- 

 moving animal, and has been confounded with the species called 

 tardigradus, although doubtless a much more agile creature. 

 See Plate II. figs. 5, and 6. 



In all the quadrupeds before mentioned, the other blood- 

 vessels, as well as the nerves, presented the common appear- 

 ances. The size of the heads, and the interior capacity of the 

 skulls, both in the Bradypus tridactylus and the Lemur tardigradus, 

 seemed smaller in proportion than is usual among animals, so 

 that the quantity of brain must be less than ordinary. 



The effect of this peculiar disposition of the arteries, in the 

 limbs of these slow-moving quadrupeds, will be that of retard- 

 ing the velocity of the blood. It is well known, and has been 



