126 



THE MECHANICAL FUNCTIONS OF THE FOOT. 



dilatation is slight, and, in fact, in narrow-heeled feet con- 

 traction may replace the normal expansion. The greatest 

 obstacle to dilatation, however, is shoeing, inasmuch as it 

 removes the counter pressure of the ground to a greater or less 

 extent, and prevents the horny sole, horny frog, and bars 

 performing their functions in the same degree as they other- 

 wise would. In horses working on hard roads it has been 

 recommended to employ pads of rubber, so as to transmit the 

 counter pressure of the ground to the sole and frog, and so 

 promote dilatation, but the advocates of this plan overlook the 

 fact that pads press continuously on the frog, and that much of 

 their beneficial action is thus lost. 



Figs. 71 and 72.— Right fore-foot seen from below and above. The dotted 

 lines show the changes in form which occiu" at the moment of extreme 

 extension of the fetlock joint. 



3. Movements of the Sole. — The horny sole becomes flatter 

 under the body-weight, most distinctly at the posterior parts 

 of the sole, and least so at the toe and towards the periphery. 

 The width of the hoof and thickness of the horny sole are of 

 considerable importance in determining the extent of this 

 movement, the descent of the sole being greatest towards the 

 heels in flat and spreading hoofs. A proof of the changes in 

 form of the hoof may be found in the bright and sometimes 

 excavated friction surfaces at the heels of the shoe. Peters 

 says these prove the existence of two movements of the bearing 

 surface of the hoof, that occurring in the longitudinal direction 



