502 VOLUNTARY MOTION. 



which it had penetrated from side to side ; and when it is considered that the 

 animal was then moving through a medium even a thousand times more dense 

 than that through which a bird cleaves its course at different heights of the 

 atmosphere, and that this was performed in the same direction with the ship, 

 what a conception do we form of this display of muscular power !" (On Mus- 

 cular Motion. Select Dissertations, p. 281.) Muscular strength is proportion- 

 ally much greater in smaller animals. " A flea can draw from seventy to eighty 

 times its own weight, whereas a horse cannot draw with ease more than three 

 times its own weight." (1. c. Haller, El. Physiol. L. ix. S. iii.) 



A flea weighs less than a grain, and will clear an inch and a half at a leap ; 

 and Americans have calculated that if a man, weighing about 150 pounds, could 

 leap in proportion, he would be able to spring 12,800 miles, and so jump with 

 ease from New York to Cochin China. 



In some animals of very slow motion, as the tardipedes, the chief artery of 

 the extremities is found split into many parallel trunks, instead of remain- 

 ing as one and branching forth. (Sir Anthony Carlisle, Phil. Trans. 1810.) 

 In the fore leg of the lemur tardigradus, sixty brachial arteries exist. The con- 

 nection between this circumstance and slow motion is unknown. 



