Preparation of Study Skins and Skeletons

Preparation of Study Skins and Skeletons

This activity must be supervised by qualified science educators. There are inherent safety problems, including infectious disease, that must be provided for. Only the basic outline is provided on this web page. Users outside The Science Room must assume complete responsibility for the safety and success of those involved when using this activity.

Preparation of a museum mount (small skin).

The Cotton Rat, Sigmodon hispidus, is a perfect size for beginners and is easy to catch. Smaller mice are harder for the beginner but possible to do. Note: beginners should not use a rabbit. The skin is thin, tearing easily and the hair comes out easily. A ball of oats and peanut butter is the bait of choice. The smallest Hav-a-Hart traps (10 X 3 X 3) are great, but regular mouse or rat traps (snap traps) will work, They are, however, hard on skulls. Set them in the grass along a fence and near water. You will usually be successful overnight.

The finished mount lays flat on its belly, with the front feet down and the back feet up. The ART of taxidermy is beyond the scope of this class.

Working with fresh animals is best, but the animal can be frozen until time for skinning. Be sure it is completely thawed before starting.

The only incision is from the middle of the belly to the base of the tail. With experience, the length of this incision can even be decreased. The smaller the incision, the better the mount will look.

Use a blunt instrument, such as a very dull solid steel scalpel, to separate the skin from the muscle. Work the knee-joint of the hind legs up through the incision. The less the skin is pulled, the less it will stretch. The less it stretches, the better the mount will look. When a knee-joint is through the incision, cut the joint. A pair of small dissecting scissors works well. When both knee-joints are cut, work around the base of the tail. When all of the tail is exposed where it attaches to the muscle of the body, catch the muscle of the tail with one hand and the sheath of the tail with the other hand. Pull on the muscle of the tail. It will, with some difficulty, slip out of the sheath.

The skin can now be taken off the body much like taking off a sock. Use the blunt instrument to separate skin and muscle. Try not to stretch the skin.

The next trouble spot is the front legs. Find the knee-joints and cut them.

A detailed explaination of how to do the head is almost impossible. Stay as close to the skull as possible. Watch the ears first, then the eyes, the mouth, and finally the nose. When the nose is free, the skinned body is on one side and the inside-out skin on the other.

If this is done properly, there is NO blood. If the first incision goes too deep, it can get messy. Yellow corn meal is the best thing to use to soak up the blood. You can't use too much. It will also take blood off the hair if the blood spot is rubbed with corn meal. The corn meal will shake or brush off easily.

The only "chemical" needed on the inside of the skin is Twenty Mule-Team Borax, right from the laundry section of the supermarket. Rub the inside of the skin with this and any flesh remaining on the skin will ball-up and easily rub off the skin. Rub the flesh on the leg bones and the bones come clean. Don't worry about the feet.

While the skin is still inside-out, sew the mouth closed.

Now turn the skin right-side-out. Fill the skin with cotton; one piece for the head, one for the body, and wrap the leg bones. Quilting cotton is less expensive than sterile cotton. Synthetic is not as good as regular, but will work. Paper towels can even used, in a pinch. Use a piece of wire in the tail sheath. Let it extend into the body area for support.

Finally, close the belly incision.

As the skin dries, it will shrink. To keep the mount straight, pin the skin to a piece of heavy cardboard. A piece of index card paper clipped on each side of each ear will prevent them from curling. The mount will be dry in about a week. Be sure it is dry before removing the pins. The larger the skin, the longer to dry.

The mounts will keep in a case with moth flakes. Stored in this manner, they will last indefinately. They will last for years even without the moth flakes.

This procedure will work well for animals up to about eight pounds. Anything larger should be done as a flat skin.

Preparation a flat skin:

Active trapping of animals larger than rodents is NOT encouraged for high school students. Local hunters or trappers can provide larger animals, IN SEASON. Road-kill animals can be used if not too mutilated or too RIPE. As long as the hair does not "slip" (come out in your hand when pulled) the animal is not too ripe.

Lay the animal on its back. Make a single cut from the base of the throat to the end of the tail. Extend the cut from the throat to the corner of the mouth.

From the midline, cut ninety degrees along the inside of each leg to the wrist.

Here a decision must be made about leaving the feet on the skin. If a skeleton mount is planned, the feet cannot be left on the skin. Cut the skin all the way around the wrist. If a skeleton mount is not planned, keep the feet on the skin because it will make a better looking skin. Cut the wrist joint, not the skin. Unless the feet are very large, do not try to skin them. The feet will usually dry without special treatment.

Those are the major cuts. Now just work the skin away from the muscle. Some animals, like the opossm, have a layer of fat between the skin and muscle. This makes the process harder. This layer has to come off the skin, now or later. The cleaner the skinning process, the less work later.

Once the skin is off, remove any blood from the hair with yellow corn meal. Stretch the skin and tack it to a board with the hair toward the board. It is important to make the skin very tight. When this is done, use a dull instrument to "flesh" the skin. After all the large bits of flesh are removed, rub the skin with Twenty Mule-Team Borax. This will remove any remaining flesh.

Working a small amount of alum into the skin will help hold the hair. This is very important if the animal was not "fresh".

All that is needed at this point is cover the skin with salt and let it dry. The skin will last a very long time if kept dry. It is worth the chemical danger to high school students to use other preservatives.

Again for the safety of students, using chemicals to remove the hair, like buckskin, or to soften the skin is something best left to professionals.

Skeleton preparation is a smelly and time consuming process. A successful experience requires committment!

Once an animal is skinned, the internal organs must all be removed. The carcass is then sectioned into small enough pieces to fit the largest "cooking" container available. Boil the carcass until the flesh is ready to "fall of the bones". Think of the task like deboning a chicken, except keep the bones, not the meat. A pure soap, like Castle Soap, or a small amount of ammonia, can be added to the water before boiling. This will help soften the flesh, but also increases the smell. Do not use a detergent!

Removing the flesh from the bones is easier when the flesh is hot, but timing is usually hard to accomplish. It can be done with cool flesh, but do not refrigerate. It is important to keep the bones organized as the flesh is removed. It will be hard to decide which bones go to which legs, for instance, if they are mixed up before puting the skeleton together.

When the bones have been cleaned, cover them with 40% cream peroxide developer. This is available in any good health and beauty shop. The peroxide will remove any remaining non-bone material and whiten the bones. Leave the cream on the bones until white. Unlike the 50% bleach solution used in the "old days", peroxide will not hurt the bone - so the cream can be left over night, if needed. After the bones are white, wash them completely. Let the bones dry COMPLETELY before attempting to glue the bones together.

Now comes the fun part. Think of it as a 3-D puzzle. A picture of a complete skeleton can be helpful. Use a sturdy wire to run from the inside of the skull to the pelvis. String the vertebrae onto this wire. Two wires will support the skeleton on some type of base, one between the front legs and one between the rear legs. The vertebrae are glued together when all are in place on the wire. The classic glue is regular Elmers White Glue. A good super glue gel or hot glue makes the work much easier because the bones are held in position for a few seconds, instead of several minutes. Elmers still has its place. It is very good for filling gaps or repairing breaks. Elmers will make the strongest and most rigid bonds between the bones. Hot glue makes the weakest bonds. Super glue gel is somewhere in between.

When the vertebrae and head are on the wire, mount this part of the skeleton to the base. This serves as a platform to attach the appendicular skeleton. Ribs go on next, then the hind legs, the tail, and finally the front legs.

There are all kinds of little tricks to make assembly easier that are not covered here. Discovering them for yourself should add to the fun. ENJOY.