124 



THE MECHANICAL FUNCTIONS OF THE FOOT. 



tendons exercising pressure on tlie plantar cushion. As tbe 

 latter is closely connected with the lateral cartilages and com- 

 pletely fills the upper depression of the horny frog, it tends to 

 drive apart the quarters and to cause the bulbs to swell, while, 

 as the horny frog now rests on the ground, it contributes to this 

 dilating effect. In the shod hoof, however, the horny frog is not 



always in contact with the 

 ground, or at least not through- 

 out its whole extent ; it is, 

 therefore, easy to understand 

 oc why the expansion of the hoof 

 is more marked at tbe coro- 

 nary border than at the bear- 



FlG. TO.^Vertical cross section of foot seen from iug SUlfaCC of the liecls. It 

 behind (this section has been made nearer the ^, ■, i ^i^i„4- 



heeis than fig. 69). o, posterior part of plantar must also DC remembered that 



cnshion ; h, median ridge of frog; c. lateral i r? t i j ^ i. 4-^ 1-.,. 



cartilage ; (7, horn wall ; e, lateral face of frog; hootS Whcn SllOQ arS apt tO DC 

 /", point of union between the bars and frog. t j 4.x £ ^ ^,,u. 



■ ' ^ very dry, and the frog poorly 



developed, or diminished by excessive paring or by disease, and, 

 therefore, dilatation at the bearing surface is often difficult 

 to detect. These considerations go far towards explaining the 

 somewhat common, though erroneous, belief that the bearing 

 surface of the heels is incapable of dilatation. 



All parts of the foot, not even excepting the os pedis, are 

 elastic, although not to the same extent. The os pedis is least 

 elastic ; then comes the horny wall, horny sole, horny frog, 

 lateral cartilage, plantar cushion, coronary band, cutis, and sub- 

 cutis. The posterior half of the hoof allows of the greatest 

 change in form ; a fact which explains the frequent occurrence 

 of disease of this portion of the foot under the influence of 

 severe work, neglect of the hoof and faulty shoeing. 



1. Movement at the Coronary Border (fig. 72). — While the 

 horse stands equally on all four feet, the anterior and lateral 

 parts of the coronary border, and especially the points opposite 

 which the wall forms an acute angle with the earth, are in a 

 condition of tension and incline to contract. At the posterior 

 part, where the wall forms an obtuse angle with the ground, 

 there is a tendency to dilatation. When considerable weight 

 is placed on the foot, that is, during backward and downward 

 movement of the fetlock, a slight contraction occurs in the 

 anterior parts of the hoof, and extends backwards to a varying 



