Name: _______________________________
Biology
Rat #1: I Smell a Rat!
5.8.12
Etiquette:
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Name your new buddy. It gave its life to you so that you can expand your horizons.
These are the same tools surgeons use. Treat them with the utmost respect.
You cannot be too serious during a dissection.
Never have a point or blade facing up.
Absolutely no food or drink while your rat is out.
Never stick anything into the blue tray pads except for pins.
Don’t gesticulate or tug on anything with a blade in your hand.
If you must walk with a blade in your hand, do it with the blade pointing downward.
Leave your tray and tools in better shape than when you received them.
Relative Body Positions:
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Anterior = towards the head
Posterior = towards the tail
Dorsal = towards the back
Ventral = towards the stomach
Medial = towards the midline
Lateral = towards the sides
Proximal = towards the center of the body
Distal = away from the center of the body
External Features:
A hairy coat covers most of the rat’s body. Note the sensitive vibrissae (whiskers) on
the face. The nares (nostrils) are at the anterior of the head. The front teeth are called
incisors and the rear teeth are molars. The eyes bulge from the head and enable the rat
to see in almost all directions at once. Eyes equipped with large pupils are one of many
adaptations to nocturnal life. The nictitating membrane is located at the inside corner of
the eye. This translucent membrane may be drawn across the eyeball for protection.
Locate the eyelids – they are similar to those found in humans. Ears are on the
posterior of the head and are composed of pinna (external ear) and an ear canal.
On the ventral surface of the rat are six pairs of nipples. The tail is located on the
posterior and is covered with hair and scales. Ventral to the base of the tail is the anus.
Female rats will have a clitoris, a urinary aperture (opening), vaginal opening and a
vulva. Male rats will have a pair of scrotal sacs which contain the testes which produce
sperm cells. The testes may be withdrawn into the abdomen during non-reproductive
periods. The penis is located just anterior to the scrotal sacs.
The rat is a quadruped (four feet). Both the sole and heel of a rat’s foot contact the
ground as indicated by the lack of hair from the toes to the heel.
Skin Your Rat:
1. This might require two people. Don’t be shy.
2. Lay your rat on its dorsal surface with the tail toward you. You will need scissors,
scalpel, and patience to remove the skin without damaging the underlying muscles
and organs. An incision was already made in the throat to inject colored latex into
the circulatory system.
3. Snip anterior from this incision toward the lower lip (see handout). Do not cut
deeply! Cut only the integument (skin).
4. Snip posterior along the ventral midline to the genitals (external sex organs).
5. Cut through the skin in a circle around the genitals and continue the midventral
incision to the tail.
6. Cut a circle around the base of the tail.
7. Make four more incisions on the ventral surface from the midline to the two ankles
of the hind legs and the two wrists of the forelegs.
8. Cut through the skin in a circle around the wrists and the ankles.
9. To separate the skin from the body, grasp the flap of skin extending from the chest
under a forelimb, and force the tip of a blunt probe between the skin and the
connective tissue holding the skin to the body. This connective tissue is called fascia
and is tough yet flexible.
10. Work slowly, and gently peel the skin from the body.
11. Remove the skin until you expose the ventral surface of the chest and abdomen.
12. Work toward the dorsal surface. Notice that thin sheets of muscle attach to the
skin.
13. When you have detached the skin to the dorsal midline, begin to peel the skin
toward the base of the skull. You may notice a deposit of fat between the shoulder
blades. This is brown fat and is specialized for heat production if the animal is
stressed by low temperatures.
14. Do not remove the skin from the face.
15. Leave the skin attached at the base of the skull, and use it as a protective cape to
wrap your specimen when you are not studying it.