OF THE EXTERIOR ?>P 449 



are stronger than those which produce the opposite motion. 

 Those of the two sides of the body which produce the lateral 

 inclination, and the rotation round the axis of the body, pre- 

 sent only the slight difference which is generally observable 

 between the two sides of the body. The others present much 

 more important differences. Borelli thought that the flexors 

 were shorter than the extensors, and that contracting with an 

 equal force, they necessarily draw the bones in flexion. 

 Richerand also thinks that the difference is in favour of the 

 former; Meckel has adopted this opinion: these two physiolo- 

 gists are of opinion that this difference is established on the 

 observation of the bent attitude that is assumed by every part 

 of the body in a state of repose, and that its cause exists in the 

 force and length of the muscles, in the volume of their nerves, 

 and in the more favourable disposition of the flexors, relatively 

 to the centre of motion, and to the direction of the bones. 



Ritter has added to these differences that the flexors contract 

 when the positive pole of the galvanic pile communicates with 

 the muscular extremity of the nerve, and the negative pole 

 with the central extremity; and that the contrary obtains with 

 the extensor muscles. This difference, doubtless, is a mere 

 difference of galvanic susceptibility ; a susceptibility sufficiently 

 powerful in the strongest muscles, to cause them to contract 

 under the least favourable circumstance of the galvanic action. 



Roulin* thinks with Borelli, that the principal cause of an- 

 tagonism between the flexors and extensors depends on their 

 respective length, and consequently on their tension. 



This question perhaps merits being considered in a more 

 general manner; the predominance must be sought in the 

 length and in the volume of the muscles, and more properly 

 in the number of fleshy fibres that enter into their composi- 

 tion- it must also be sought in the disposition of the muscles 

 relatively to the levers on which they act ; it is necessary to 

 observe what the attitude is that the parts take in their most 

 ordinary action, and that which they take in repose, during 



* See Recherches sur fa mouvemens et ks attitudes de thomme, dans k 

 journal de physiologic, Vol. I. et II. 



