386 



Mr Appleton, The Influence of Function 



adductors should prove full of interest. The postacetabular part 

 of the pelvis shows in its modifications in various groups an 

 attempt to provide the semimembranosus, etc., with more effective 

 leverage (notably in Artiodactyla), as judged on these principles. 

 Lowering (or lengthening) the postacetabular pelvis vastly increases 

 the effective leverage of hamstring muscles. The changes in the 

 feraorococcygeus, its transference to the tuber ischii and knee in 

 cursorials, the migration upwards of the biceps in the catarrhines, 

 are all explainable on these lines. 



Fig. 5. AB and ^Sg^femur of Semnopithecus. Ab and ^4B3=femur of Gorilla, re- 

 duced to same ^C yl(7 = postacetabular pelvis. In positions of great extension, 

 ABg, ASg, semimembranosus to knee is almost useless as an extensor in any but 

 flexed positions or positions near AB. The most effective position for an ex- 

 tending adductor lies up near head of femur, represented by a muscle CX^ 

 (relatively lower on the shaft of the gorilla). The muscle CX has to shorten 

 itseK CXg to 0-4 of its length at CX, but muscle CB is CB^ only shortened 0"1 

 of its length. 



Shortening of the femur in cursorials is explained by Gregory* 

 as an adaptation which allows of more "open angles of insertion" 

 of hip-extensors and other muscles. As a matter of fact, in ordinary 

 locomotion, the femoral attachments are the fixed points or origins 

 of the muscles; and their effective leverage on the hip-joint will be 

 lessened by shortening of the femur. The shortening appears to me, 

 considered only from this point of view, to be a disadvantage. 

 Gregory is in difficulties over explaining the lengthening of the 

 femur in the recent greyhound and racehorse. Perhaps they lengthen 

 to increase the effective leverage. 



* Gregory, Annals of the New York Academy of Sciences, vol. xxii, p. 291. 



