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 matter 
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. Benaviour or THE Sotze.—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 LATERAL CARTILAGES.* 
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.V.S., in the 
Veterinary Record, vol. v., p. 38. 
