384 



Mr Appleton, The Influence of Function 



internus is rendered possible, increasing power and diminishing 

 range of movement. 



There appears then abundant reason to beheve that pecuhari- 

 ties of shape of the femur cannot be properly understood without 

 reference to the muscles attached and adjacent thereto. And 

 further, that the muscles themselves have been evolved in accord- 

 ance with the habits of an animal and of its forerunners. 



Effective Leverage as a factor in Muscular Specialisations. 



, A consideration of the mode of action of the Adductor* group 

 shows that in cursorials and saltatorials their function is largely 

 one of hip-extension. The adductor function proper is more char- 

 acteristic of arboreal types with a wide range of abduction. 



A Cavia. 



B Lepus. 



C Bos. 



Fig. 4. Lengths AB, AC, are proportional to lengths of femur and postacetabular 

 pelvis in various types. (Used merely as a diagram) 



A. (Cavia porcellus) illustrates in ABj^ position of thigh in which semimembrano- 

 sus obtains maximum effective leverage, measured by perpendicular AC to joint 

 A. AC is greater than AD, which measures leverage when thigh occupies 

 position AB. 



B. (Lepus cuniculus) when extension proceeds further till thigh is in position 

 AB2, leverage is again less, AD^ being less than AC. At this time, a shaft ad- 

 ductor CZ2 is acting to the test advantage. 



C (Guernsey cow) all positions of flexion in front of the vertical AB require 

 use of the lowest, viz. the knee adductors, which only attain their maximum 

 power at ABj^ {ACB^ being a right angle). At same point of extension AB^ at 

 which rabbit employs shaft conductor CZg , the cow is still employing CP^ 

 adductors attached close to the knee. 



Considering extension alone in the first place, the maximum 

 effective leverage can be easily shown {e.g. for a semimembranosus 

 or ischio-condyloideus) to obtain when the muscle is at right 

 angles (Fig. 4 a) to the hne joining acetabulum with tuber ischii. 

 If the thigh is at right angles to the pelvis, the most effective 



''' Including semimembranosus. 



