88 



HORSESHOEING. 



and presses the perforans tendon down upon tke plantar cushion. 

 The plantar cushion being compressed from above, and being un- 

 able to expand downward, is correspondingly squeezed out 

 towards the sides and crowded against the lateral cartilages, and 

 they, yielding, press against and push before them the wall at 

 the quarters. The resistance of the earth acts upon the plantar 

 surface of the hoof, and especially upon tlie frog, and it, widen- 

 ing, crowds the bars apart, and in this manner contributes to 

 the expansion of the quarters, especially at their plantar border 

 (see Fig. 90). The horny sole under the descent and pressure 



of the OS pedis sinks a 

 little — that is, the arch 

 of the sole becomes 

 somewhat flattened. All 

 these changes are much, 

 more marked upon 

 sound unshod hoofs, be- 

 cause in them the re- 

 sistance of the earth 

 upon the sole and frog 

 is pronoimced and com- 

 plete. These changes in 

 form are more marked 

 in front feet than in 

 hind. In defective and 

 diseased hoofs it may happen that at the moment of greatest 

 weight-bearing, instead of an expansion a contraction may 

 occur at the plantar border of the quarters. 



Three highly elastic organs there are which play the chief 

 part in these movements, — ^namely, the lateral cartilages, the 

 plantar cushion, and the homy frog. Besides these structures, 

 indeed, all the remaining parts of the horn capsule, especially 

 its coronary border, possess more or less elasticity, and con- 

 tribute to the above-mentioned changes of form. 



In order to maintain the elastic tissues of the foot in their 

 proper activity, regular and abundant exercise, with protection 



Vertical, transverse section of a foot seen from behind: 

 A, OS coronae; B, os navicularis; C, os pedis; a, lateral 

 cartilage; 6, anterior portion of fleshy frog; c, section of 

 perforans tendon; d, suspensory ligament of the navicu- 

 lar bone; /, wall; m, sole; n, white line; o, frog. 



