002 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



the kind of preparation, the vessels are filled with more than ordinary success. The 

 arteries alone are injected ; and the peculiarity of their arrangement is to be ob- 

 served in the axillary arteries, and in the iliacs. These vessels, at their entrance 

 into the upper and lower limbs, are suddenly divided into a number of equal-sized 

 cylinders, which occasionally anastomose with each other. They are exclusively 

 distributed on the muscles ; while the arteries sent to all the parts of the body, 

 excepting the limbs, divide in the usual arborescent form ; and even those arteries 

 of the limbs which are employed on substances not muscular, branch off 

 like the common blood-vessels. I counted 23 of these cylinders, parallel 

 to each other, about the middle of the upper arm; and 17 in the inguinal fasci- 

 culus. 



This fact appeared at first too solitary for the foundation of any physiological 

 reasoning; but having since had an opportunity of prosecuting the inquiry among 

 animals of similar habits and character, I have been encouraged to hope that the 

 result may eventually assist in the elucidation of muscular motion. The bradypus 

 tridactylus, or great American Sloth, has a similar distribution of the arteries of 

 its limbs to that already described in the lemur tardigradus. The communications 

 of these vessels with each other are more frequent than in the lemur tardigradus, 

 and their number is considerably greater. I counted 42 separate cylinders on the 

 superficies of the brachial fasciculus; and from the bulk of the fasciculus I estimate 

 that there were 20, or more, concealed in the middle. The lower extremity has 

 its arteries less divided, and they are of larger diameter. I observed only 34 

 branches in the middle of the thigh; and the first series of ramifications were 

 larger than the subsequent ones. May not this have some relation to the greater 

 distance of the lower limb from the heart? The extremely slow movements of 

 the bradypus tridactylus 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; 

 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 

 arrangement, 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 universally represented quicker than those of the bradypus tri- 

 dactylus. 



The Lemur Loris was next examined, and its arterial system was found to resemble 

 those already described ; but, as the animal had been preserved in very strong spirit, 

 the vessels were so corrugated as not to admit of injection. The 2 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, though doubtless a much more agile creature. 

 In all the quadrupeds before mentioned, the other blood-vessels, as well as the 



