24 On some Elementary Principles in Animal Mechanics. [June 17, 



in character, from wasting during the last illness, I determined to test the 

 question by experiment, and accordingly selected a fine Pyrenean Mastiff 

 for the purpose, which I killed by strychnia, and dissected immediately 

 after death, with the following results, which were obtained, as before, by 

 noting the specific gravities of the muscles and tendons, and by weighing 

 a measured length of each : — 



Cross sections of Muscles and Tendons in a Pyrenean Mastiff, and ratios 



of same. 





Cross section of 



Cross section of 



Eatio of cross 



Name of muscle. 



muscle, in 



tendon, in 



section of muscle 





square inches. 



square inches. 



to that of tendon. 



1. Gastrocnemius 



2-631 



0-0520 



50-6 





0-283 



0-0059 



48-0 



3. Fl. dig. long 



0-195 



0*0045 



43'3 





0-632 



0-0160 



395 





0-176 



0-0056 



314 



C. Fl. hall, long 



o-68o 



• 0-0228 



29-8 





0-909 



00449 



20'2 



8. Fl. dig. subl 



0-319 



0-0251 



I2"7 



9. Fl. dig. prof. 



0-902 



0-0830 



IO9 



10. Ext. carp, uln 



0181 



0-0197 



9 -2 



These results, obtained from measurements made upon a freshly killed 

 animal, confirm those found from observation of the human subject, and 

 prove that the ratio of the cross section of the muscle to that of its tendon 

 depends upon the amount of friction experienced by the latter, the co- 

 efficient being greater in proportion as the friction is less. 



The following observations, made upon a Wallaby Kangaroo, confirm in 

 a general way the preceding results : — 



Cross sections of Muscles and Tendons in a Wallaby Kangaroo, and ratios 



of same. 





Cross section of 



Cross sect ion of 



Eatio of cross 



Name of muscle. 



muscle, in 



tendon, in 



section of muscle 





! square inches. 



sq uare inches. 



to that of tendon. 





... r 3 i 3 



0.0356 



3 6 "9 



2. Fl. long, dig 



• • o-354 



0-0246 



144 



It appears from the preceding investigation that the cross section of a 

 muscle does not bear a constant ratio to the cross section of its tendon, 

 unless the friction experienced by the muscle and tendon be also constant, 

 and that there may even be a surplusage of strength in the tendon beyond 

 what is absolutely necessary to resist the combined force of the muscle and 

 friction. This surplusage, however, cannot be supposed to be large, if the 

 principle of economy of material in nature be admitted. 



