on the Conformation of Bones 387 



What, then, has brought about the shortening of the typical 

 cursorial femur {e.g., Artiodactyla [Gregory])? I think it is to be 

 found in the enormous strain thrown upon the knee extensors in the 

 active animals with long femora. The longer femur when the knee 

 is flexed puts an almost impossible burden on the vasti during a 

 violent thrust from the tibia. In large animals it is inadmissible; 

 the femur shortens. Confirmation of this is found in the enormous 

 size of the vasti in Tarsius (see Table II), a small-sized jumper with 

 long hmb-segments. The larger jumpers, the kangaroos, exhibit 

 distinct shortening of the femur. It is better to develop the neces- 

 sarily powerful hip muscles than to depend on powerful knee 

 muscles ; the centre of gravity is, in fact, thus placed so much the 

 higher up the hmb. 



Considerations of the actual shortening (Fig. 5) undergone by 

 muscles passing to the higher and lower parts of the femur re- 

 spectively in fully extended positions, would suggest that muscles 

 do not all present the same percentage shortenmg over the com- 

 plete range of hip movement. If all shortened by the same fraction 

 of their length they would effect different ranges of hip movement, 

 distally attached muscles causing extensive angular movements, 

 proximally attached muscles small ones. Comparative study of the 

 internal structure of the Great Adductor will, it is hoped, prove 

 enlightening. 



