in the Arteries of slow-moving Animals. 101 



explained by various writers, that the blood moves quicker in 

 the arteries near the heart, than in the remote branches ; and 

 also, that fluids move more rapidly through tubes which branch 

 off suddenly from large trunks, than if they had been propelled 

 for a considerable distance through small-sized cylinders; 

 besides which, the frequent communications in the cylinders of 

 the Brady pus tridactylus must produce eddies, which will retard 

 the progress of the fluid. From these and a variety of other 

 facts, which it is not necessary to specify, it will appear, that one 

 effect upon the animal economy, connected with this arrange- 

 ment of vessels, must be, that of diminishing the velocity of the 

 blood passing into the muscles of the limbs. It may be difficult 

 to determine, whether the slow movement of the blood sent to 

 these muscles be a subordinate convenience to other primary 

 causes of their slow contraction, or whether it be of itself the 

 immediate and principal cause. The facts at present ascertained, 

 relative to muscular motion, do not authorize me to treat de- 

 cidedly of the share which the vascular system holds in the 

 operation of muscular contraction. Certain it is, that a larger 

 proportion of arteries is sent to the muscles of quadrupeds, than 

 to the ordinary substances ; and the extreme redness of these 

 organs shews that their capillaries are of large diameter. A 

 greater degree of redness is also observable in those muscles 

 (of the same animal) which are most frequently called into 

 action. The habits of life among the tardigrade animals, give 

 occasion for the long continued contraction of some muscles in 

 their limbs : these creatures are represented clinging to the 

 boughs of trees, and remaining thus, without locomotion, for 

 several hours. The powers which require so long a time to 

 determine the contraction of a series of muscles, are probably 



