External Features of the Rat

1. External Features of the Rat • This presentation is accompanied by a handout- “Skinning Your Rat” • As you identify each structure, complete the question on the handout. • Underlined words will be subject to identification on the test. • Don’t guess correct answers, use the rat guide (pgs. 6-14) for assistance. TIP FOR SUCCESS….. MAKE SURE YOU ARE STUDYING EACH STRUCTURE AND ITS FUNCTION AS YOU GO ALONG.

2. Set Up • Remove the dissection tools and paper towel from the dissection tray. • One partner should glove up. Wear tight fighting gloves. The other partner will run the computer. • Your teacher will bring each group a rat. There will be a female rat and a male rat at each table so work together. • Open the bag containing the rat with the paper scissors, not the dissecting scissors.

3. Color The albino or common brown rat, Rattusnorvegicus, will be used for the study of the body systems including the integumentary system. Note the color of your rat and answer questions 1 and 2. TIP FOR SUCCESS…Discuss each question with your lab partner.

4. Body Regions • Find the following body regions shown in the picture. • Complete the matching (3-8) on your handout.

5. Cranial Region • Note the nasal openings (nostrils), the triangular mouth, and the chisel like incisor teeth. Rats are gnawing mammals, and these incisors will continue to grow for as long as the rat lives. • Answer questions 9 and 10. Are you remembering to use your “Rat Dissection Guide”?

6. Cranial Region continued Note the hairy coat that covers the rat and the sensory hairs (whiskers) located on the rat's face, called vibrissae. Answer question 11. Sometimes your notes will come in handy.

7. Cranial Region continued Note the eyes with the large pupil and the nictitatingmembrane found at the inside corner of the eye. The eyelids are similar to those found in humans. Answer question 12.

8. Cranial Region continued The external ear consists of the pinnaand the external auditory meatus(ear canal). Answer question 13. Sometimes your book will help you answer questions.

9. Limbs Study the fore and hind feet. Observe the claws and plantar tubercles. Answer questions 14 -17.

10. Pelvic Region Near the base of the tail, find the anus, the posterior opening of the digestive tract. If you have a male rat, you will have to lift the scrotum to find the anus.

11. Pelvic Region- Female Now work with your table partners. In the female, the reproductive and excretory (urinary) systems open separately to the exterior. The vaginal orifice is nearest the anus and lies between the anus and the urinary orifice which is situated on an elevation.

12. Pelvic Region- Male Continue to work with your table partners. In most males the scrotum appears as a prominent swelling below the anus. Midventrally, near the anterior end of the scrotum, is the urogenital(reproductive and urinary) opening. Insert one blade of the scissors into the opening and cut a short distance. This will reveal the penis, the exposed end of which is the glans penis, surrounded by the foreskin or prepuce. Label the reproductive structures (18- 23.)

13. Abdominal Region Continue to work with your table partners. Check for teats on both sexes. Answer question 24.

14. Tail Study the tail. Answer questions 25-26.

15. Clean Up! 1. Spray the rat with preservative.

16. Clean Up 2. Double bag the rat -first the bag it came in -second a zip-lock with your names and hour clearly listed -or 2 zip-lock bags

17. Clean Up • Wash your tray and dissection instruments in the prep room. Don’t be pokey. Everyone needs to get to class on time.

18. Clean Up! 4. Dry your tray and instruments. 5. Leave a dry clean lab area for the next group. 6. Rats are kept in your tray in your cabinet.

19. Finish the lab Label the picture of the rat on your handout using key underlined words. Circle the words associated with the integumentary system.