82 
THE VETERINARY SCIENCE 
it be even pressed upon, for it is very sensitive. When a 
nail has been driven so as to injure this membrane it is a 
common expression to say "you have pricked that horse's 
foot." 
2. The Sole. — The sole is a thick plate of horn which helps 
to form the under part of the hoof. It is situated between the 
inner border of the under part of the wall already mentioned and 
the front of the frog. The under part of the sole is concave, or 
hollowed out. The upper part of the sole is attached to the 
under part of the os pedis bone, or bone of the foot, by a 
membrane called the quick, or sensitive sole — this membrane 
is merely a continuation of the sensitive laminae. The outer 
part of the sole is attached to the inner part of the wall 
When pared down a white ring is seen where the sole and 
the wall is united. At the back part of the sole there is a 
notch the shape of the letter V; in this notch the frog is 
situated. It is important to remember when shoeing never 
to let the shoe rest on any part of the sole; neither is it 
well to pare off too much of the barky-looking substance of 
the sole, as this helps to keep the moisture in the foot. When 
this is taken off it allows the moisture to escape and the hoof 
becomes dry and contracted. 
3. The Frog. — The frog is the prominent spongy horn 
found in the V-shaped notch in the back of the sole. It is wide at 
the back and helps to form the heel of the foot ; the pointed part 
in the front is called the apex of the frog. The under part of 
the frog is triangular in shape and has a hollow in it called 
the cleft of the frog. There is a hollow at each side of the 
frog, between it and the bars, called the commissures of the 
frog. On the upper part is a membrane, known as the sensi- 
tive frog, which attaches it to the under part of the os pedis, 
or foot bone. This membrane is simply a continuation of 
the sensitive sole spoken of in connection with the sole. The 
back part of the frog is the widest part and spreads out 
to form the heel. 
To obtain the best idea of the structure of the foot, get 
a hoof and the bones of the leg as far up as the fetlock, and 
saw them down through the center. This will show the 
exact conformation. The shape of the hoof differs ; large 
draft horses are apt to have what is termed a flat foot, while 
in road horses the chief trouble is what is known as con- 
tracted feet and weak heels. 
