iionsKsnoKiNd. r)87 



as a soft and very elaslii- wedjjf betwft'ii the bars iiiul between the 

 edges of the sole just in front of the bars. A broad and sliaUow de- 

 pression in its center diviiK's it into two branches, which diverge as 

 they i)ass backward into the horny bulbs of the heel. In fiont of the 

 luidille cleft the two i)iiinches unite to foiui the body of the fi'og, 

 which entls in the point of the fiog. The bar of a bar shoe shouhl 

 rest on the branches of the frog. In unshod hoofs the bearing edge 

 of the wall, the sole, frog, and bars aiv all on a level; that is. the 

 under surface of the hoof is perfectly flat, and each of these structuies 

 assists in beaiing the boily weight. 



With respect to solidity, the ditlerent parts <tf the hoof vary 

 widely. The middle layer of the wall is hardei- and more tenacious 

 than the sole, foi* the lattei* ciumbles away nr pa.^ses otf in larger or 

 smaller flakes on its undei- surface, while no such spontaneous short- 

 ening of the wall occurs. The white line and the frog are .soft-hoin 

 structures, and differ from haid hom in that their hoin cells do not 

 under natural conditions become hard and h(»rnlike. They are very 

 elastic, absorb moistuie rapidly, and as I'eadily dry out and become 

 hard, brittle, and easily fissured. Horn of good (|uality is fine 

 grained and tough, while bad horn is coarse graint'd and either 

 mellow and friable or hard and brittle. .Ml horn is a j^oor con- 

 ductor of heat, and the harder (drier) the hoiii the more slowly 

 does it transmit extremes of tt'inperatme. 



THE PHYSIOLOGICAL MOVEMENTS OF THE HOOF. 



A hoof while supporting the body weight has a different form, and 

 the .structures inclosed within the hoof have a different position than 

 when not bearing weiglit. Since the amount of weight borne by a 

 foot is continually changing. :md the i-elations of internal pressure 

 are continuously \arying, a foot is. from a physiological viewj^oint. 

 never at I'est. The most nniiked changes of form of the hoof occur 



when the foot U'ars the git-atest weight, iia ly. at the time of the 



greatest des<-ent of the fetloclv. Hriefly, tlies(> changes of form are: 

 (1) \i\ expansion (u- widening of the whole back half of the foiU 

 from the coronet to the lower edge of the <iii:irter^. This expansion 

 varies between one-fiftieth and one-twelfth of an inch. ('2) A nar- 

 n)wing of the fiont half of the foot, measured at the c(U'onet. (3) A 

 sinking of the heels and a flattening of the wings of the sole. The.M' 

 changes are more marked in the half of the foot that bears the 

 gieater weight. 



The changes of form occur in the following ordei . When the foot 

 is set to the ground the body weight is transmitted through the bones 

 and .sensitive an<l horny leaves to the wall. The coflin Ixme and 

 navicular bone sink a little and rotate backward. M the suuu- time 



