64 ANIMAL LIFE 



toes. Any bending of the knee, therefore, tightens the 

 hold of the feet ; and this hold is rendered still more 

 secure by another tendon which runs at the back of the 

 leg and divides into three one for each toe. When 

 the bird perches, the weight of the body thrusts the 

 knee out and the ankle back, and simultaneously 

 tightens both sets of tendons, and through them the 

 hold of the feet. 



In swimming-birds this flexure is the means whereby 

 the membrane between the toes is opened and brought 

 to bear on the water ; but, in order that the resistance 

 of the feet may be overcome, when the forward 

 stroke is to be made, the membrane is rendered 

 capable of opening and shutting, and the toes are 

 spread out during the swimming, or back-stroke, and 

 brought together during the forward one. In a 

 grebe's foot the vanes down the toes can be pulled 

 out flat by the back tendon and turned down vertically 

 by the front one. The foot of a bird, no less than 

 any other part of its body, gives evidence of the 

 most exquisite finish and usefulness. 



REFERENCES 



Animal locomotion : Pettigrew, J. B., ' Inter. Sci. Series,' 

 vol. vii. Marey, * Animal Mechanism.' Ibid. vol. xi. 



Flight: Headley, F., 'The Structure and Life of Birds.' 

 Macmill m. 



