ANATOMY OF VERTEBRATES. 



muscles on the heel-bone, fig. 37, k, the action is that of the second 

 kind of lever, in which the resistance (of the tibia on the astraga- 

 lus), as in fig. 32, w, is between the fulcrum F (afforded by the 

 ball of the hallux), and the power a (tcndo achillis). 



31 



A y B 



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32 



F 



w 



Lever of the first kind. 



Lever of the second kind. 



In lifting a weight in the hand by motion of the fore-arm only, 

 fig. 33, the elbow-joint is bent ; the power (of the flexors of the 

 fore-arm) being applied (as by the biceps, />) at a, between the 

 fulcrum (elbow-joint)^ and the resistance w or b, according to the 

 third kind of lever exemplified in fig. 34. 



The mechanism of the pulley is exemplified in the passage of the 

 tendons of the peronei muscles through the groove of the external 

 malleolus of the human ankle-joint, in the tendon of the obturator 



33 



interims gliding through the groove in the os ischii, in the tendon 



_ 



of the circumflexus palati passing through the hamular process ot 

 the sphenoid bone, in the tendon of the obliquus superior gliding 

 through the ring attached to the frontal bone, and -in several 

 other instances where a change of the directions of the limbs 

 results from tendons passing over joints, through grooves in 



