MOTION AND LOCOMOTION 



91 



crane, where also the weight is supported on the end 

 of a tapering shaft ? A glance at Fig. 44 shows us 

 that the material of the steel frame is arranged so 

 as to support any such weight, and counteract the 

 tendency to sheer off the head of the crane 

 Similarly, if we examine 

 the head of the femur, 

 the bone substance will 

 be found to be arranged 

 on an exactly similar 

 plan, as we see from a 

 comparison of Figs. 44 

 and 39. 



Lastly, the edges of flat 

 structures, e.g., leaves of 

 plants; are often strength- 

 ened bystrands of skeleton 

 tissue and these strands 

 are aided by the veins, 

 which are usually ar- 

 ranged, in broad leaves at 

 all events, in a series of 

 successively smaller arches 

 from the midrib outwards 

 (Fig. 45). Large leaves 

 which have no such 

 strengthened margins are 

 liable to be torn to ribbons by the wind, very much 

 in the same way as a flag is frayed out unless 

 protected by a marginal cord. 



FIG. 45. Venation at the edge 

 of a leaf. 



