382 Mr Appleton, The Influence of Function 



influenced by the presence of a long flange-like third trochanter 

 the requirements of muscular attachments are obvious. In fact 

 the shaft in the small primitive types may be regarded as consisting 

 of a pillar for strength and an external flange for muscular attach- 

 ment, as in the eocene Meniscotherium and others. The great 

 width in the extinct Megatherium is probably of a similar nature : 

 X-ray investigation of the primitive femur of Priodontes supports 

 this view of its nature. 



In larger and more active animals increase of stress requires a ; 

 stouter femur; there is now less need for flanges. Also, as Scott | 

 has shown, all heavy types, despite their relative want of activity, 

 show a general tendency to reduction of the external flange and 

 third trochanter in situ {e.g. elephant). Data do not appear avail- 

 able to show whether reduction of the superficial gluteus, or of the 

 vasti, can account for such loss in the elephant. 



The descending extensor ridge already mentioned is developed 

 in association with a peculiar muscular combination. That it has 

 also the advantage of withstanding stress from the forwardly pro- 

 jecting great trochanter which in these animals (e.g. Tarsius, 

 Priodontes) forms a conspicuous attachment for the vastus ex- 

 externus, is suggested by X-ray examination of the bone*. 



The actual bulk of the vastus externus is probably closely 

 related to the degree of projection of the third trochanter, from 

 which the fibres of gluteus superficiaUs pass upwards and forwards 

 across it. A third trochanter placed lower down the shaft will 

 tend to be longer. 



The term "frontal pilaster" applied to this ridge by Pearson 

 and Bell suggests a comparison with the pilaster on the back of a 

 human femur: only so long as both are regarded as adaptations 

 for muscular attachment does the term seem justifiable. 



The human "pilaster," to which the adductors are attached, 

 was regarded by Manouvrier as being due to the backward exten- 

 sion of the crureus muscle, on the outer side; and to expansion of 

 the front of the bone. How is it that in Tarsius, with far larger 

 knee extensors, this backward encroachment does not occur? It 

 is an example of the influence exerted by the M. femorococcygeus, 

 which in primitive types is attached to the outer margin of the 

 flattened femur. A distinct line is produced which marks also the 

 attachment of the crureus, vastus externus and adductors, the 

 attachment in fact of the external intermuscular septum. A similar 

 fine for attachment of the vastus internus is found along the inner 

 margin. These lines may for convenience be termed the 

 External and Internal septal lines. While the M. femoro- 

 coccygeus isattached to the femoral shaft, the external 

 s epta nine never gets displaced to the back of thefemur. 



* Bono trabeculae may be considered indicative oflines of Pressure (Murk Jansen). 



