A STUDY IN FOOT STRUCTURE. 



AUSTIN GARY. 



The material and the direction of this study were suggested 

 to me by Professor W. B. Scott of Princeton, and during its 

 progress I have been much indebted to his candor and helpful- 

 ness. The original plan was to select a short phylogeny contain- 

 ing well-marked changes, and to study that closely, with the 

 idea of drawing any conclusions possible as to the genesis of 

 bone structures. The basis of the work is the manus of a Peris- 

 sodactyl from the Bridger eocene Palaeosyops [Limnohyops], an 

 animal of tapirine proportions ; while the White River genus 

 Menodus has been used for comparison. Menodus was a slow- 

 gaited form, with heavy body and head. It was undoubtedly 

 derived from a form closely resembling Palaeosyops, and the 

 two serve practically as a phylum. 



The foot of Palaeosyops is a beautiful specimen with very few 

 imperfections. Its articular surfaces are mostly simple, many 

 being nearly plane, while they are generally strongly inclined 

 to the axis of the digits. These peculiarities render this foot 

 amenable to geometrical study, a method suggested and ren- 

 dered valuable by recent arguments, based on palaeontological 

 material, for the mechanical evolution of structure. This method 

 has in fact been applied. The volume of the bones was first 

 got at. Next the area of the bearing surfaces and their inclina- 

 tion to the digits were measured. Then, giving to the thrust 

 of each metacarpal a value proportional to its volume, the dis- 

 tribution of that thrust can, by resolution and composition of 

 forces, be traced through the foot, and the pressure on each 

 surface and bone approximately obtained. Conditions of course 

 do not admit anything like exactness, and only general results 

 are given. A diagram is given later on, illustrating the method, 

 which through the foot has been applied as carefully as seemed 

 advantageous or possible. 



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