on the Conformation of Bones 375 



possible to draw the line between pathology and physiology. Cer- 

 tain observations from human orthopaedic surgery throw light on 

 this question. 



Human bone-grafts grow in thickness under certain conditions of 

 stress. Els* has recently stated that a thick bone-graft diminishes 

 in girth till it resembles the bone it replaces. The repair, again, of a 

 fracture is assisted by the transmitted pressure obtainable when 

 a calliper-splint is used. The internal structure of an astragalus 

 changes under gross alterations of mechanical stress as occur in flat- 

 foot. The observations of Dendy and Nicholson! oi^ the spicules 

 of sponges suggest also the continual hving reaction of skeletal 

 elements to mechanical factors. 



When therefore we recall Hunter's observation that during 

 growth there must be a continual remodelhng of the neck of the 

 human femur, we find ample grounds for supposing that one's 

 habit of walking, or pecuharities of musculature, or of the methods 

 of employing it, Mall probably play an important part in the pro- 

 duction of individual variations. 



Much valuable information is provided by Pearson and Bell 

 in the vast array of statistics in their recent monograph on the 

 femur of mediaeval Londoners and of Primates. They show that 

 while there is a considerable correlation between dimensions of 

 epiphyses of the femur, and between these and its total (and 

 shaft) length, this is much less evident in the female, in whom also 

 the (upper) epiphysis shows less variation in absolute size. On the 

 other hand, and this seems very important, the correlation of coronal 

 and sagittal diameters of the shaft is quite small, and of the neck 

 diameters smaller still. This appears to me just what one would 

 expect from the incidence of "environmental" factors, affecting 

 diameters in different ways. The assumption that such are here- 

 ditary features, evolved by selection, is unnecessary. The different 

 correlations and variabilities on the two sides may be accounted 

 for by muscular peculiarities, asymmetrical locomotion, and un- 

 usual habits. 



Could we but anticipate the differences of right from left which 

 may appear in the rising generation of to-day with its ''scooters" 

 and differentiation in function of lower limbs ! 



Musculature and Cursorial Specialisation. 



By some means many groups have evolved cursorial types 

 with similar muscular characteristics. The Primitive type of thigh 

 musculature was doubtless of the pattern found in the living tree- 

 shrew (Tupaia) and the lemurs. Matthew, in fact, suggests an 

 arboreal ancestry for mammalia. 



* Els, Anatom. Hefte, 1 Abt. 176 Heft. 58 Band, Heft 3, 1920. 

 t Dendy and Nicholson, Proc. Royal Soc. Lxxxix, B, 1917, p. 573. 



