THE SKELETON OF THE HIND-LIMB 55 



mobility. Environmental conditions could not com])ine 

 to free the hind-limb of its duty of .su])])orting tlie l:)ody 

 weight and yet preserve it in full functional activity; 

 the arboreal habit did this for the fore-limb, but there 

 was no life circumstance that could do the same thing 

 for the hind-limb. An aerial life might, at fir^jt sight, 



Fig. 19. — Diagrammatic Comparison of the Skeletal 

 Elements of (A) Hind and (B) Fore Limb. 



seem to fulfil the necessary conditions, and flight might 

 seem to afford an escape from the supporting servitude 

 of the hind-limb. Flying Mammals have achieved many 

 interesting modifications in hind -limb structure, but they 

 have not successfully emancipated a hind-limb to give it 

 other and more highly educational functions. They have 

 avoided making it a mere prop only to convert it into a 

 suspending hook. The hind-limb of the Bats is worthy 



