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the HOOF

make sure to read p 595-600 of Dyce for the horse foot information.

antlers/horns...do you know the difference? 

horn: specialized skin structure overlying bone.
antler: hair


regular old epidermis always has some kind of supporting dermis and this 
dermis is very vascular. on top of the dermis are the germinal epidermal 
cells and then all the layers of the epidermis and in regular keratinized 
skin you end up with plaques of keratin flaking off the top

fingernails are specialized skin types...

the dermis can be specialized...there can be papilla, an undulating type 
situation of dermis :), or it can develop in a laminar type situation, 
where instead of just forming the finger type projections, it formsa 
whole bunch of folds

so you have flat type, tubular/papillary type, and laminar type.


HORN develops as a bony projection from the skull. there is normal skin 
at the base, and then there is the tubular type of dermis covering the 
rest of the horn. covering the dermis is the tubular horn.- and the 
intertubular horn. this is hard keratinized epithelium. in a small horn 
the bony core is solid. in older animals it does kind of hollow out and 
communicate with the frontal sinuses. bovidae have horns. horns are 
usually a simple projection, except for the prong horned antelope.

blood supply to horn is through the vessels in the dermis- between bone 
and horn (epidermis).
both male and females have horns

ANTLER

found in the cervidae. there is a pedicle of bone on the skull, and on 
top of that is a projection off the pedicle which continues to grow
blood supply to the antler is from within the velvet, a specialized 
epithelium which covers the antler. then when the animal rubs off the 
velvet

antlers are male characteristic, females don't have them. they are 
regulated by testosterone. antlers are shed every year. the male deer in 
the fall will rub off the velvet and they will devascularize, also 
testosterone level falls, and this causes the velvet to slough as well, 
and the antlers will fall off. antler core is 50% less mineralized than 
bone.

BOIS means WOOD in french and also means ANTLER :)

usuallly L and R antler fall off at the same time.


so. how do you make a "horn" into a "nail" or a "hoof" or a "claw" ???

If you boil a skull that has a horn on it, you macerate the soft tissue, 
and you can pull the horn off the horn bone because the dermis is gone. 
the same thing would happen with a horse hoof and a human fingernail.

anyone who's been prodded by a horn knows the horn is hard stuff.
like any keratinized tissue, it is not sensitive. deep to the horny 
epithelium, there IS innervation, however. dehorning is usually done with 
nerve blocks.

HUMAN FINGERNAIL.

the germinal epithelium is found near the cuticle area. the nail itself 
is tubular and intertubular keratinized epithelium. the dermis is deep to 
the germinal epi and also underlies the nail itself and covers Piii in a 
laminar arrangement...see handout. the dermis has lamina which 
interdigitate w/lamina coming down from the keratinized epithelium of hte 
nail itself. this locking mechanism is what actually holds the nail on. 
so how does the nail grow forward, then, if it's locked into place? 
well,the dermis is stationary. the growing nail slides over the lamellar 
epithelium. the epidermis over the deep laminar projections of the dermis 
sloughs off its keratinized covering, and this allows the nail to slip on 
by, tearing off some of this deep tissue with it. nails grow about 
.5mm/week.

antlers grow about an inch a day.


so main nail growth happens at cuticle, and nail grows distally sliding 
over the dermal lamina.

DOG CLAW very similar to fingernail but laterally compressed. it grows in 
the same way, slipping over the lamina.

note that the coria are the same as dermises.

the periople

in people, you have the cuticle, and this is analagous to the equine 
periople. the perioplic tissue grows down to the toe as the stratum 
externum, a shiny sheetlike covering of the hoof.



HOOF
the CORONET is a regional term describing the region of transition from 
skin to hoof wall. hoofwall is just the specialized horny epidermal 
tissue, of course.

at the level of the coronet is a band of dermis projecting out into 
terminal papillae, and from this dermis the hoof wall grows distally.

the coronary dermis (coronary corium) is the "base" of the hoof tissue.
the hoof grows from proximal to distal. distal to the coronary dermis 
deep to the hoof wall is the laminar dermis, which terminates as the 
solar dermis.
just like in the fingernail, there are lamellae holding the hoof to the 
bone. the insensitive lamina of the hoof wall interdigitate with the 
sensitive lamina of the deep dermis.

the Piii bone has many holes in it because there is a rich vascular 
network. 

there are hundreds of lamina holding the hoof to the dermis.

laminitis: inflammation of sensitive lamina...causes hoof to rip off.

NON-VITAL HOOF: stratum externum (periople), stratum medium (thick part 
of hoof wall), stratum internum (insensitive lamina)

solar corium develops into sole of foot. frog corum becomes frog.

the largest part of hoof comes from coronary region.
slides: dyce.

note that the extensive vascular network of the hoof is also useful in 
absorbing shock.


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