70 



ANIMAL MECHANISM, 



can contract. But, whatever may be the absolute value of 

 this contraction, it is always in proportion to the length of 

 red fibre ; that is the result of the nature of the phenomena 

 which produce work in the muscle. 



Thus, every muscle whose two points of attachment are 

 susceptible of being much displaced by the efiect of contrac- 

 tion, must necessarily be a long muscle. On the contrary, 

 every muscle which has to produce a movement of short 

 extent must of necessity be a short muscle, whatever may be 

 the distance which separates the two points of attachment. 

 Thus, the flexors of the fingers and toes are short muscles ; 

 but they are furnished with long tendons, which convey even 

 to the phalanges of the fingers or toes the slight movement 

 originated at a considerable distance at the fore-arm or the leg. 



It is easy to estimate, in the dead body, the extent of the 

 displacement which a muscle can exercise on its two points of 

 attachment. By producing the movements of flexion or 

 extension in a limb, we can ascertain with sufiicient exact- 

 ness the extent by which they separate or draw together the 

 osseous attachments of its muscles. In a recent skeleton we 

 can also judge with sufiicient accuracy of the amount of these 

 movements by the extent to which the articulated surfaces 

 can glide over each other. 



In examining the muscular frame of man we are struqk 

 with the extreme length of the sartorius muscle ; it is easy 

 to be seen that no other can displace to such an extent its 

 points of bony attachment. The sterno-mastoidal and the 

 magnus rectus abdominis are, after this, the longest muscles ; 

 these also are muscles which have very extensive movements. 

 We might thus cause all the muscles of the organism to pass 

 under review, and in them all we should see that the length 

 of the red fibres corresponds with the extent of the movement 

 which this muscle has to execute. But, in the study, we 

 must be on our guard against a cause of error which would 

 tend to arrange certain short muscles among those which are 

 longer. 



Borelli himself has noticed this cause of error; he has 

 shown how penni/orm muscles, that is to say, those whose 

 fibres are inserted obliquely into the tendon, like the barbs of 



