66 DISEASES OF THE HORSE'S FOOT 



to expansion exists, but the change of form first becomes 

 measurable in the region where the lateral cartilages begin. 

 Quite posteriorly the expansion again diminishes. 



Fig. 37, a, by the dotted line represents the expansion at 

 the moment of over-extension of the fetlock-joint. This 

 expansion is itself rather less than at the coronary edge, 

 and it shows itself distinctly only when the weighted hoof is 

 exposed to a counter-pressure on the sole and frog, no mat- 

 ter whether the counter-pressure is produced naturally or 

 artificially. Thus anything tending to the removal of the 

 pressure from below, such as a decayed condition of the 

 frog or excessive paring in the forge, will diminish the 

 extent of expansion of the solar edge. 



Contraction of the solar edge of the heels occurs at the 

 moment of greatest over-extension of the fetlock-joint — 

 that is, in a foot with pressure from below absent. On the 

 face of it, this appears impossible. Lungwitz, however, 

 has perfectly demonstrated it; and, when dealing with the 

 functions of the lateral cartilages in a later paragraph, we 

 shall show reason for why it is but a simple and natural 

 result of the foot dynamics. 



3. Behaviour of the Sole. — The horny sole becomes 

 flattened under the action of the body-weight. This is 

 most distinct at the solar branches, and gradually shades 

 off anteriorly and towards the circumference. As might 

 be supposed, width of hoof and thickness of the solar horn 

 exert an influence on the extent of this movement. The 

 sinking of the horny sole is most marked in flat hoofs. 



D. THE FUNCTIONS OF THE LATEEAL CABTILAGES.* 



We have just referred to contraction of the heels as 

 taking the place of a normal expansion in those cases 

 where ground frog-pressure was absent. We shall readily 

 understand this when we bear in mind the anatomy of the 

 parts concerned, especially that of the plantar cushion. 



* Extracted from a paper by J. A. Gilruth, M.R.C.S.V., in the 

 Veterinary Record, vol. i., p. 358. 



