1869.] Principles in Animal Mechanics. 23 



Muscles. 



Sp. gr. 



Biceps humeri {long head) 1*050 



Biceps humeri 1*054 



Brachialis 1*053 



Mean 1*0523 



Tendons. 



Scapular tendon of biceps 1*112 



Radial tendon of biceps 1*119 



Mean 1*1155 



From these specific gravities it was easy to determine the cross section 

 of either muscles or tendons, by weighing a kuown length of either one 

 or other. In this manner the following Table was constructed : — ■ 



Cross sections of Muscles and Tendons in an Adult Human Male Subject, 

 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. 





o-8 95 



0*0317 



28-2 





0-148 



0-0050 



26-4 





0-584 



0*0223 



26-2 





0-405 



0-0220 



18-4 



5. Biceps humeri (long head) 



0-379 



0-0212 



180 





0-228 



0-OI45 



157 





0-234 



0-OI55 



151 





0-212 



0-0199 



10-7 



9. PL dig. subl 



0-618 



0*0665 



93 



10. Fl. dig. prof. 



0*768 



0-0928 



8-3 



11. Ext. oss. met. poll 



0*223 



0-0289 



77 



12. Fl. carp, uln 



0-182 



0-0254 



7-2 



From the preceding Table, it appears that the ratio of the cross section 

 of the muscles to that of the tendons may range from 7 to 28, or be four 

 times greater in one case than another. We may also see in general, that 

 the tendons exposed to the greatest amount of friction have the smallest 

 coefficients of cross section. Thus the radial tendon of the biceps has a 

 coefficient of 28 2, while the scapular tendon, which undergoes the friction 

 of passing over the head of the humerus, has a coefficient of 18*0. Again, 

 the Ext. oss. met. poll., whose tendon winds round the radius, and has the 

 duty imposed upon it of binding down the tendons of the radial extensors 

 of the wrist, has the coefficient of 7*7, as compared with 26 2 and 18*4, 

 the coefficients of the comparatively free tendons of these extensors. 



As it might be objected that the relative cross sections of muscle and 

 tendon, in a human subject that died a natural death, might be exceptional 



