281 



curately in that plane ; this indeed is a result to be expected 

 in a hinge joint like the knee, for otherwise there would be a 

 constant wrench produced on the joint, by the unbalanced ro- 

 tation outwards or inwards. 



Of the muscles that flex the knee joint, the biceps, semimembrano- 

 sus, and sartorius were found to act in the plane of the joint, 

 while the semitendinosus abducted at an angle of 5° 40', and the 

 gracilis adducted at an angle of 8°. 



A little consideration will serve to show, provided my postulates 

 be admitted, that the semitendinosus wrenches the joint by a ro- 

 tation inwards, represented by its weight multiplied by the sine 

 of the angle its plane makes with the plane of motion of the 

 knee joint; and that the gracilis wrenches the joint by a rota- 

 tion outwards, represented by a similar quantity. 



Hence we find 



Wienchmgrnomentinwardsof semitendinosus = 0*61 x sin 5° 40' = 0-06 oz. 



,, outwards of gracilis = 0*55 x sin 8° =0-07 oz. 



These two wrenching moments nearly balance each other, so as to 

 leave little or no strain on the joint; and it is probable that the 

 slight difference between them is compensated by the action of 

 the poplitcdus, which aids the semitendinosus to some extent. 

 The flexors of the leg are well shown in Tig. 23, which represents 

 them all in their natural positions, with the exception of the 

 biceps, which has been drawn out of its place, in order to show 

 better the position of the remaining muscles. 



21. M. gastrocnemius, 0-89 oz. 



22. M. solceus, 0-63 oz. 



23. M. plantar is, 0-18 oz. 



24. M. flexor digitorum longus, . . 0-36 oz. 



25. M. tibialis posticus, 0-30 oz. 



26. M. flexor hallucis longus, 0-66 oz. 



27. M. accessorius, 0*05 oz. 



The tendon of the flexor hallucis divides, in the centre of the sole, 

 into tendons distributed to the 3rd and 4th toes, and an- 

 other tendon which constitutes half the tendon of the hallux. 

 The tendon of the flexor digitorum divides at the same point into 

 tendons distributed to the 2nd and 5th toes, and another 

 tendon which constitutes the remaining half of the tendon of the 

 hallux. 



The M. accessorius tendon meets all the foregoing at the point of 



subdivision ; but its largest branch is continued directly on, into 



the tendon of the flexor hallucis. 

 The distribution of the flexor tendons to the toes varies in different 



genera of Monkeys. 

 In the Cebus, their distribution is like that of the Macacus neme- 



strinus, viz., flexor hallucis to 3rd, 4th, and half the hallux ; 



