448 MUSCULAR MOTION. 



the os humeri to the trunk, to exert a degree of traction upwards, and 

 thus to assist the extensors of the feet in the projection of the body. 

 It is with this view, that the ancients employed their 0,7.*^*$, or poisers 

 in leaping; and that the moderns use bricks, stones, or other solid heavy 

 bodies with a like intent. It is likewise manifest, that by steadying 

 the arms, and then moving them rapidly backwards, a backward im- 

 pulse may be given to the upper part of the trunk. 



The effect of a run before we leap is to add to the force developed 

 by muscular contraction that of the impulse acquired by the body whilst 

 running. The leap is, under such circumstances, necessarily more 

 extensive. 



Some of the smaller animals surprise us by the extent of their leaps. 

 The jumping maggot, found in cheese, erects itself upon its anus, forms 

 its body into a circle, by bringing its head and tail into contact, and, 

 having contracted every part as much as possible, unbends with a sud- 

 den jerk, and darts forward to an astonishing distance. Small animals 

 leap much farther than the larger in proportion to their size; and, as 

 Mr. Sharon Turner has remarked, 1 "exhibit muscular powers still more 

 superior to those of the greatest animals than their comparative minds." 

 He has given amusing representations of this difference: for example, 

 Linnaeus observes, that if an elephant were as strong in proportion as 

 a stag beetle, he would be able to tear up rocks and level mountains. 

 A cock-chafer is, for its size, six times as strong as a horse. 2 The flea 

 and locust leap two hundred times their own length, as if a man should 

 leap three times as high as St. Paul's. 3 The cuckoo-spit froghopper 

 sometimes leaps two or three yards, which is more -than two hundred 

 and fifty times its own length, as if a man should vault at once a quarter 

 of a mile. 4 Mouffet 5 relates, that an English mechanic made a golden 

 chain as long as a finger, with a lock and key, which was dragged by 

 a flea; and Latreille 6 mentions a flea of moderate size dragging a silver 

 cannon on wheels, that was twenty-four times its own weight. This 

 cannon was charged with powder and fired, without the flea seeming to 

 be alarmed. 



c. Running. 



This variety of progression consists of a series of low leaps per- 

 formed by each leg in alternation. It differs from walking, in the body 

 being projected forward at each step, and in the hind-foot being raised 

 before the fore-foot touches the ground. It is more rapid than the 

 quickest walk, because the acquired velocity is preserved and increased, 

 at each bound, by a new velocity. Running, therefore, cannot be in- 

 stantaneously suspended, although a stop may be put to walking at any 

 moment. 



In running, the body is inclined forward, in order that the centre 

 of gravity may be in a proper position for receiving an impulse in that 



' Sacred History of the World, Amer. edit., p. 372, New York, 1832. 



4 Kirby and Spence, Introduction to Entomology, Amer. edit., p. 486, Philad., 1846. 



3 Nat. History of Insects, i. 17. 4 Insect Transformations, v. 6, p. 179 



s Theatr. Insect, 275. 



6 Nouv. Diet. d'Histoire Natur., xxviii. 249, and Kirby, op. cit. 



