1. Read the Background Information and Answer Questions 1-4 of Your Lab Sheet

Procedure for Dissection: 1. Read the Background information and answer questions 1- 4 of your lab sheet. 2. Follow the steps of the dissection, label the diagrams and answer the questions on your lab sheet. 3. Follow the clean up steps. 4. Take the quiz on the rat structures 5. Remember to sit down if you feel sick! Part1: Rat Dissection Background

Mammals are vertebrates having hair on their body and mammary glands to nourish their young. The majority are placental mammals in which the developing young or fetus, grows inside the female’s uterus while attached to a membrane called the placenta. The placenta is where the food and oxygen for the fetus diffuses out of the mother’s blood stream into the fetus’s blood stream, and wastes from the fetus diffuse to the mother. Young mammals generally need care when they are born and for a long time afterward. During this period, they are cared for by one or both parents. Maternal care is an important mammalian characteristic. Parental care helps ensure that young mammals will survive and reproduce.

The dissection of the rat is important because rats and humans have the same level of metabolism and have similar organs and systems.

The digestive system is a great example of similarities between rats and humans. Food is chewed first in the mouth, then swallowed and carried through the esophagus to the stomach. Once properly churned, food moves into the beginning of the small intestine where the liver and pancreas add important digestive chemicals. As food travels through the small intestine nutrients are absorbed through the lining of the intestine and sent to the blood stream. At the end of the small intestine, food enters the large intestine where the remaining water is absorbed back into the body. Lastly, the remaining material exits the body through the anus. The entire process takes between 24- 72 hours depending on the individual. Part 2: External Anatomy

1. Examine the rat’s head. Locate the eyelids, and the external ears (pinnae). Find the nostrils, the whiskers, the tail, and the mouth. Label these structures on your External Structures diagram.

2. Study the rat’s appendages. Locate the front foot (mannus) and the hind foot (pes). Label these structures on your diagram.

3. Lift the tail to find the anus. Label this structure on your diagram.

4. Determine the gender of your rat. Male rats will have an obvious scrotal sac which contains the testes right at the base of the tail, often covering the anus. Females lack this sac. Record the gender of your rat on #4 your lab sheet.

Part 3: Internal anatomy of Abdominal cavity:

5. Send one person to grab two pieces of string. Send one dissector to watch Miss Walker demo step 6

6. Lay the rat ventral (belly) side up and tie one string on the mannus and another string on the pes of one side. Wrap each string around the back of the tray and then tie it to the opposite mannus and pes. Be sure to pull the string tight before making your knot. The point is to have the rat tightly held down so it doesn’t slide around while you are dissecting.

7. Send one dissector to watch Miss Walker demo step 8-9

8. Use the forceps to pinch a fold of skin in the very middle of the belly and use the scissor to make a shallow snip just through the skin, revealing the muscle underneath. Now use the scissors to cut through the wall of muscle in a line up the center of the body to the ribcage and down to between the legs. Be careful not to snip really deeply, or you will damage the organs! Hold the scissors horizontally as you cut. Don’t point them down ward.

9. At the rib cage, cut down the sides of the body. Between the legs, cut up around the legs and then down the sides of the body. This should allow the abdominal wall to be spread open, revealing the organs. Pin the walls of the body to the tray.

10. Identify and label on your internal structures diagram the diaphragm, the liver, the stomach, the small intestine, the large intestine, and the spleen. They are all on the lower half of the diagram

11. Send one dissector to watch Miss Walker demonstrate step 12-14

12. Use the scissors to carefully remove the large and small intestine. Identify the kidneys and bladder.

13. If you have a female, identify the ovaries, and then go look at a male rat and identify the testes.

14. If you have male, you will need to carefully use your scissors to snip down into the scrotal sac to identify the testes. Then go look at a female rat and identify the ovaries.

Part 4: Internal Anatomy of Thoracic Cavity:

15. Send one dissector to watch Miss Walker demo step 16-17

16. Using the scissors, cut through the left and right side of the rib cage and the across the top. Carefully snip the membranes surrounding the heart and lungs, and then remove the rib cage entirely.

17. Identify the heart, and the right and left lung. Label these structures on your diagram.

18. Begin clean up. The assigned cleaner will assign each group member one of the jobs to do. Use the clean up checklist to make sure everything is finished properly. Make sure waste is placed in the appropriate trash can.

19. At the end of clean up, you will take a quiz on the structures we have identified today. Answer the analysis question 5 using what you have seen today. 19. Carefully use the scissors to cut through and remove the muscles of the neck. This should reveal a whitish shiny tube which is the trachea. Note the rings of cartilage in the trachea which keeps it from closing. Behind and underneath the trachea is the esophagus. It connects the mouth to the stomach. Label these two structures on your diagram.

20. Using your scissors, carefully remove the heart from the rat. Cut the heart vertically in half. Identify the right atrium, the right ventricle, the left atrium, and the left ventricle. Label the diagram of the heart on your lab.

21. Begin clean up. The assigned cleaner will assign each group member one of the jobs to do. Use the clean up checklist to make sure everything is finished properly. Make sure waste is placed in the appropriate trash can.

22. At the end of clean up, you will take a quiz on the structures we have identified today.