BIOLOGY. 299 







which latter undergo friction at the wrist and other joints of the 

 hand, the force being applied by the muscles to the tendon above 

 the wrist, and the resistance being applied at the extremities of 

 the tendons below the wrist by the object grasped by the hand. 

 From the principle of *' Least Action in Nature," we are entitled 

 to assume the strength of each portion of a tendon to be propor- 

 tional to the force it is required to transmit; and since, in a proper 

 hand, these forces are continually diminished by friction, as we pro- 

 ceed from the muscle to the fingers, we should expect the strength 

 of the tendon above the wrist to be greater than the united 

 strength of all the finger-tendons. Conversely, in a proper foot, 

 the force is applied by the ground to the extremities of the ten- 

 dons of the toes, and transmitted to the flexor muscles of the leg, 

 by means of the tendons of the inner ankles, which undergo 

 friction in passing round that and the other joints of the foot. In 

 this case, therefore, we should expect the united strengths of the 

 flexor tendons of the toes to exceed the strength of the flexor 

 tendons above the heel. In the case of the hand, friction acts 

 against the muscles ; in the case of the foot, friction aids the mus- 

 cles. I have measured the relative strengths of the deep flexor 

 tendons of the hand above and below the wrist in several animals, 

 and also the relative strengths of the long flexor tendons of the 

 foot above and below the ankle, in the following manner : I 

 weighed certain lengths of the tendons above the wrist and ankle, 

 and compared these weights with the weights of equal lengths of 

 the flexor tendons of the fingers or toes, assuming that the 

 weights of equal lengths are proportional to their cross sections, 

 and these again proportional to the strengths of the tendons at the 

 place of section. The difference between the weights above and 

 below the joint represents the sum of all the frictions experienced 

 by the tendons between the two points of section. Tables are 

 given showing the results of measurements, for example, in the 

 case of the Pyrenean mastiff the amount of friction is 65.4 per 

 cent., while in the Boomer kangaroo it is nil. The foregoing 

 animals all realize the typical idea of a true foot, with a variable 

 amount of friction at the ankle-joint; this friction disappearing al- 

 together in the Boomer kangaroo, whose method of progression 

 realizes absolute mechanical perfection, as no force whatever is 

 consumed by the friction of the flexor tendons at the heel. The 

 only animals whose feet deviated from the typical foot were 3, 

 namely, the alligator, common porcupine, and phalanger. In 

 these animals the foot has the mechanical action of a hand, or 

 grasping organ ; and the flexor tendons above the ankle exceeded 

 those below the ankle by the following amount: Alligator, 11.5 

 per cent. ; common porcupine, 20.0 ; phalanger, 29.2. In the 

 case of the flexor tendons of the hand, results were obtained 

 varying from 71.0 in the case of the common porcupine, to nil in 

 the case of the goat. It will be observed that the fore foot of the 

 goat, regarded simply as an organ of locomotion, attains a per- 

 fection comparable with that of the hind foot of the kangaroo, no 

 force being lost by friction at the wrist-joint. The only animal in 

 which I found a departure from the typical hand was the llama, 



