

ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 61 



that in both the frog and tortoise different muscles are distin- 

 guished by characteristic differences in the form and process of 

 the curve of contraction. The average duration of contraction in 

 different skeletal muscles of the frog is shown in the following 

 table : 



Sec. 



1. M. hyoglossus . . . . G'2-0'3 



2. rectus abdomims . . . 0'17 



3. gastrocnemius . . O12 



4. semimembranosus . . . 0-108 



5. triceps .... 0*104 



Cash found the contraction period of Testudo europcea to be : 



Sec. 



1. M. pectoralis major . . T8 



2. glutseus . . .1-6 



3. palmaris . . . .1-0 



4. gracilis . . . .TO 



5. ,, biceps .... 0'9 



6. splenius capitis . . . 0'9 



7. ,, triceps brachii . . 0'8 

 b. retrahens colli . . . 0'75 

 9. ,, semimembranosus . . . 0*6 



10. omohyoideus . . . 0'55 



Yet more characteristic than the duration is the nature of the 

 process (form), as expressed in the myograms. Many of these have 

 such significant forms that they ought in a measure to indicate the 

 species of muscle. The accompanying figure (Fig. 3 5 A) shows 

 how differently gastrocnemius behaves from the triceps and semi- 

 niembranosus - gracilis group. These last muscles reach the 

 maximum of contraction soon after the half of their entire 

 mtraction period, while gastrocnemius takes two-thirds of its 

 iriod for contraction, and only one- third for extension. If the 

 blowing group of the most sluggish frog muscles (Fig. 3 SB) is 

 raipared with these curves, the difference is very striking. 



Fig. 35c of tortoise is even better qualified to show how 

 bhe contraction curves of different striated muscles may vary in 

 form in the same animal. M. omohyoideus contracts most rapidly 

 in correspondence with its function of withdrawing the head of 

 the animal quickly under the protecting carapace when in danger, 

 diile the powerful pectoralis major, which serves the movements 

 )f the heavy animal, " begins with an energetic lift, and delays 

 50 me time at the apex of contraction." Similar differences should 



