EXTERNAL PARTS OF THE FOOT. 
253 
the quarters and heels. This will show the necessity for 
shoeing-smiths being adepts in driving the nails, seeing the 
small space for that purpose, and more especially behind. 
The crust is thinner and a little higher in the inner than 
the outer quarter. This is another beautiful provision, 
because, being placed under the inner splint-bone, more of 
the weight rests on the inside than the outside, consequently 
it is enabled to expand more, and thus by its elasticity assists 
in lessening concussion. When, therefore, expansion is pre¬ 
vented by the inner quarter being nailed firmly to the shoe, 
corns, contraction, and sand-crack are induced. The crust 
is not liable to much variation in thickness, as will be seen 
by a reference to plate vi. fig. 10, u and v, and c in fig. 9, 
until near the top, at the coronet, or where the horn of the 
hoof unites with the skin of the pasterns, where it becomes 
abruptly thin, as will be seen on a reference to s , in fig. 10. 
Here it appears as if scooped out, and here also its colour 
and consistence are changed, and it appears like a continua¬ 
tion of the skin. This thin portion is called the coronary 
ring, r, fig. 10, which covers a thickened prolongation of 
the skin called the coronary ligament, c, in fig. 9. This 
extension of the skin is supplied with numerous densely set 
blood-vessels, connected together by a fibrous texture, many 
of which have the property of secreting the horny sub¬ 
stance which forms the crust. The sensible laminm, a, fig. 
9, have the power of secreting some horn, which furnishes 
an immediate defence against injury in cases where the 
crust is either purposely removed, or has sustained in¬ 
jury. This is sufficient proof in cases of quittor or sand- 
crack, when it becomes absolutely necessary to remove a 
portion of the crust. The exposed portion is soon covered 
by a film of a hard homy texture. The crust, however, is 
chiefly formed by the coronary ligament; and hence in 
R 
