THE MUSCLES OF THE HIND-LIMB 61 



The superficial portion of the M. pronator radii teres is 

 represented in the leg by a muscle which has long since 

 lost all power of rotation, and in Man is almost certainly 

 merged with the lateral head of the calf muscle named M. 

 gastrocnemius. 



It is clear, therefore, that these muscle groups of the 

 fore and hind limbs have undergone very dissimilar 

 changes in Man. We have seen how strangely primitive 

 is the retention of the condition of the arm ; but it would 

 seem that, in the leg, the primitive condition was departed 

 from, and that some degree of support was demanded 

 from the leg at an early stage in human evolution. With 

 a simple arrangement of anatomical parts, a slight shifting 

 of muscular origins has turned a perfectly mobile second 

 segment into a supporting segment, constructed upon 

 very simple lines. That these changes are those pro- 

 duced by the demands of support from the hind-limb in 

 tree -climbing seems obvious, since they are present in all 

 arboreal Primates, and as such we may imagine they have 

 been long established in the ancestry of Man. 



