50 



The horny frog interposes a firm resisting medium between 

 the sensitive frog and the ground. The sensitive frog com- 

 presses more readily under the double effect of superior and 

 inferior pressure. It thus lets the weight of the animal down 

 easy upon the other portions of the foot, and the instant the 

 weight is removed in the lifting movement, regains its original 

 dimensions. It is to this expansive or rebounding movement 

 that I attribute the regular, light, easy, corky, springing move- 

 ments in action that is peculiar to the horse. 



MAXIMUM AND MINIMUM OF LATERAL MOVEMENTS. 



The sensitive frog and the fissure in which it reposes are also 

 evidently constructed so as to admit of some degree of lateral 

 movement. The peculiar construction, too, of the sensitive 

 frog adapts it, I think, to receive or to resist pressure in every 

 direction, its areolae admitting of the maximum amount of rapid 

 condensation with the minimum of the lateral increase of bulk. 



SUMMARY OF VIEWS. 



Summarizing the foregoing views — the superimposed weight 

 of the animal superiorly, the solid bases afforded by the horny 

 frog inferiorly, the quarters of the horny wall laterally — these 

 are the solid resistants that call the compressive and the expan- 

 sive forces of the frog-cushion into play. More elasticity than 

 that which is inherent in these resisting structures, or any in- 

 terference with the due fulfillment of the functions of any one 

 or more of them, such as contracted quarters and a diseased 

 horny frog, would injure the structure and suspend the func- 

 tions of the primary organ of resiliency, the sensitive frog f 

 and proportionately will be the impairment of the leg or knee 

 action of the animal subject to such an abnormal condition of 

 things. 



The question of the Expansibility of the Foot is too important 

 to be dismissed with a cursory allusion. It will arise for con- 

 sideration in due course, and will then receive the attention it 

 merits. 



