10.11.96

Horse foot bones and dried hooves.

To understand the horse hoof, check out Dyce chapter 10 p 358-9. There 
are two pages on comparative anatomy of nails, claws, hooves. Also, 
smallwood has xray prints on p 247, 248, that show the anatomical 
position of the bones in a living horse. 

the bony skeleton of the hoof starts out with a metapodial (metacarpal or 
tarsal)

realize people walk plantigrade. cats and dogs walk on their toes, 
digitigrade. horses and cows walk unguligrade - walk on tip of third 
phalanx.

metapodal 
phalanx 1
phalanx 2
phalanx 3 (ungual phalanx)

the metapodeal phalangeal joint is also called the fetlock.
the proximal interphalangeal joint is the pastern (bet P1 and P2).
The distal interphalangeal joint (P2-P3) is the coffin joint.
there are proximal sesamoids at the distal caudal metapodal bone region, 
and the navicular bone is located caudally at the coffin joint.

hoof anatomy is a bit more complex. the bones above have interesting 
ligament attachments. there is also a V shaped or triangular shaped scar 
on the proximal phalanx' ventral surface, which is where one of the 
ligaments associated with the interosseus attaches, called the oblique 
sesamoidean ligament. we'll need to know this later on. 

now, the hoof - there's a thick area of the hoof at the top of the hoof, 
which horse people call the coronet. there's periople which is proximally 
very thick and rubbery, and distally is very dry and glossy, and is 
called the stratum externum, and it is a waterproofing surface for the 
hoof.  the next layer is the wall of the hoof, or stratum medium, made of 
tubular horn. this is the hardest part of the hoof. inside the hoof wall 
are a bunch of laminae, protruding in toward the center of the hoof. 
these comprise the laminar horn of the hoof. it's the laminar horn that 
interfingers w/dermis on the dorsal surface of P3 (coffin bone), and they 
hold the hoof onto the bone. so, in a sense, the horse's weight is 
hanging from it's fingernails, by these laminae. about 600 per hoof. two 
other areas of horn on the hoof. there is the bottom of the hoof, 
outlined by a horseshoe shaped hoof wall.

the lateral distal hoof wall = quarters. the heels are the most caudal 
part of the wall, which then turns in cranially forming the bars. between 
the bars is the FROG - the softest horn. note that the softest parts of 
the hoof contact the ground. the frog contains a digital cushion with a 
venous plexus. the frog must hit ground, so it can press on the venous 
plexus and push the blood out of the venous plexus. if the horse doesn't 
walk or walks with frog off ground, will get foot pathology secondary to 
blood pooling. The rest of the bottom of the hoof, between the wall and 
the frog, is the SOLE. it is made of tubular horn, intermediate in 
hardness between the horn of the wall and the horn of the frog. there is 
also a groove up the middle of the frog, and grooves at the lateral edges 
of the frog - those lateral grooves are called CUNEAN grooves, which can 
develop THRUSH, a fungal infection, if feet are not kept clean and dry. 
The sole horn is soft enough that the foot can bruise through it, but the 
sole doesn't usually touch the ground.

don't get anxious about the soft tissue anatomy. look at bones and hoof.