380 



Mr Appleton, The Influence of Function 



extends backwards round the shaft. The ridge occurs in some 

 edentates, rodents, and the Lemuroidea (including Tarsius). That 

 it does not appear in gorilla, where the superficial gluteus is at- 

 tached close up to the great trochanter and the third trochanter 

 has disappeared (as in recent Carnivora), suggests the close relation- 

 ship to this structure. 



The special tendency to development of the knee-extensors in jumpers is to be 

 seen, notably in Tarsius with its very long femur. That the M. rectus femoris (the 

 ambiens of reptiles) is not included in this development ia illustrated in the above 

 figures. 



Correlation of changes in the Femur ivith Muscular Specialisation. 



Special attention will be here directed to the form of the shaft in 

 cross-section. Much interest attaches thereto owdng to the great 

 contrast in form presented by the gorilla to the human genus. 



Unspeciahsed mammalian types generally present a trans- 

 versally oval cross-section at mid-shaft, and from the lateral 

 margin somewhere near its middle a third trochanter projects: a 

 common type in early tertiary mammaha (Pantolestes, Menisco- 

 therium, Nesodon). Cursorials and saltatorials tend to exhibit a 

 rounded shaft, and the third trochanter shifts up the femur and 

 becomes reduced or disappears. 



There is in these more active types an increase in the antero- 

 posterior diameter of the femur. I>oes this appear in adaptation 

 to the increased bending moment, tending to break the shaft 

 across, or is it merely a means of providing attachment for 

 muscles, viz. the vasti and crureus, the knee extensors? 



The more active animals do throw an enormous strain on the 

 femur in springing from the hmb when at the gallop or jump; far 

 greater than the animal's dead weight. An increase in this sagittal 

 diameter is indeed very necessary, and is the more necessary in 

 that these animals have angulated hmbs, unhke the graviportal 

 types (Gregory) with straight pillar-hke hmbs. The increased 



* Weights are given in terms of the M. rectus femoris as the unit. 



t A descending extensor ridge is present; it is no test of blood-relationship. 



