Rat Dissection
The Rat, Rattus norvegicus albinus, belongs to the Kingdom Animalia, phylum Chordata, Class mammaila, Order Rodentia, genus Rattus, and species norvegicus. The lab rat is an excellent animal for dissection purposes due to its resemblance to a human and it is a fully formed adult.
A dissection is like an operation and requires teamwork. Your team will consist of:
1.
Surgeon- person who physically makes incisions with the scalpel and forceps.
2.
Assistant surgeon- assists the surgeon.
3.
Reader- Reads instructions and directs the surgeon.
4.
Recorder- Draw and label during the dissection.




A large dissection cutting board
Surgical scissors with one blunt tip
Scalpel
Dull probes



T- Pins for holding down the skin flaps
Forceps
Ruler
At all times during the dissection it is essential that you show respect for your animal. It is also important that your specimen is sprayed with Bioshield before placing it back in the plastic bag for storage, this will prevent the tissue from drying out or becoming moldy.
Dissection is a learned skill. Some general rules to remember are: do not make deep cuts with scissors or scalpels; you may inadvertently damage underlying tissue. Know the anatomical terms such as caudal, cranial, dorsal, ventral, medial, and distal so that you can follow the directions as you study your organism.

1.
The “surgeon” and “assistant surgeon” need to put on gloves. Meanwhile, the “recorder” needs to have your storage bag labeled with your names and period.
2.
Open the bagover the sink, and carefully allow fluids to drain into the sink. Holding the rat with two gloved hands, rinse rat thoroughly under running water. Place rat onto dissecting board.
1.
Place rat side down for making external observations. Label the following major structures: Pinna -Ears, Nares -Nostrils, Eye , Vibrissae -Whiskers, Incisor tooth, Digits and Footpads, Thigh, Knee, Ankle , and Scrotum (If male). a.
Is your rat a female or a male? _______________________
In male rat, the urogenital opening is located mid ventrally in the posterior abdominal region. You should also find a large scrotal sac and anal opening under the tail. In females there are three urogenital openings. The most posterior is the anus just ventral to the tail. The vaginal opening is cranial to the anus and may be closed by the hymen in young females. The most anterior is the urethral aperture and may have a protruding clitoris. b. How many urogenital openings are in a male and female rat? Male___ Female___.

Rat Dissection
1.
You will place your rat dorsal side up on the dissecting tray. Your first incision will start at the mid back. Make an incision about 3 cm toward the tail. The objective is to cut through the skin but not into the muscle tissue. The skin of the rat is 1 to 2 mm thick.
After you see the thickness of the skin, extend incision to base of skull and to base of tail.
Pull skin away from underlying connective tissue and cut away connective tissue with scalpel so that you expose muscle. Peel skin away from muscle tissue approximately 3 cm to each side.
2.
Make an incision from the base of the neck to the ankle of the front leg. Make an incision from the base of the tail to the ankle of the hind leg. Cut through the skin and around each ankle.
3.
Place rat dorsal side down or belly side up. Make an incision from the jaw to the first urogenital opening. Be very careful not to cut into the abdominal cavity because the skin and muscle tissue is very thin in this region. Make incisions from the chest to the a ankles and from the jaw to the ankles. Also make incisions from the urogenital opening to the ankles. At this point you should be able to remove all the skin covering both the ventral and dorsal sides.

4.
Draw and label the Spinotrapezius, Latissimus dorsi, External Oblique, and Gluteus
Superficialis
Make sure that your instructor sprays your specimen with Bioshield for preservation purposes.
Place your rat into plastic bag and seal. Place dissecting tools, sharp end down into cleaning solution. With soap and water clean the dissection tray.
1.
Begin your dissection of the thoracic cavity by making an incision with your scissors at the base of the rib cage. While lifting up with the scissors (blunt end down) cut toward the chin stopping when you get between the front legs. Gently pull the incision apart and identify the diaphragm which separates the thoracic cavity from the abdominal cavity. On both sides, cut above the diaphragm toward the spinal cord. On both sides, cut from the top of the incision between the legs through the rib cage toward the spinal cord. Continue the mid-ventral incision up to the chin of the rat. From the chin of the rat, cut around the neck toward the spinal corn.
2.
Begin by identifying and removing the thymus gland. The thymus is a grayish mass that covers heart. The thymus is where T-Cells mature. The assistant surgeon should keep removed organs organized.
3.
Identify the trachea and the larynx (voice box). You may also identify the thyroid gland which regulates metabolic activity of the cells. Follow the trachea from the oral cavity down to the lungs. The right lung has four lobes and the left lung has one.
4.
The heart, covered by the pericardial sac, sits between the lungs. Remove the pericardial sac and carefully pull back the lungs so that you can identify the aorta and the vena cavas.
5.
Carefully remove the heart and all five lobes of the lungs. To do this you need to cut through all the major arteries and veins. Cut the carotid arteries near the throat and the

Rat Dissection subclavians that branch off the aorta. Trace the aorta as it raps around the back of the heart. The aorta, the inferior vena cava, and the esophagus will be bundled together with connective tissue. Try to leave the esophagus intact. Snip the trachea near the throat.
Carefully remove the heart, lungs, and trachea as one unit.
1.
Draw and label the Heart/Lung/Trachea unit removed.
Make sure that your instructor sprays your specimen with Bioshield for preservation purposes. Place your rat into plastic bag and seal. Place removed parts in a separate smaller bag. Place dissecting tools, sharp end down into cleaning solution. With soap and water clean the dissection tray.
1.
From the rib cage, insert the blunt end of the scissors and cut toward the first urogenital opening. Make a second incision from the urogenital opening laterally to the back of your specimen on both sides. Pin the flaps back to expose the abdominal cavity. If you are careful, you will see a fine membrane know as the peritoneum that covers the organs.
2.
Observe how the esophagus connects the throat to the stomach. You will need to cut through the peritoneum membrane that hold the intestines in place.
3.
The rat liver has four lobes and no gull bladder. Animals that eat constantly as opposed to intermittently typically do not have gull bladders for storing bile.

4.
Draw and label the connection between the pancreas (grayish in color), the bile duct, and the small intestine. This should be close to where the stomach connects to the small intestine. This portion of the small intestine is called the duodenum.
5.
Remove the liver. How many lobes does it have?______ What are three functions of the liver?_______________________,___________________,&_____________________
6.
Although not part of the digestive system, the spleen will be found underneath the stomach. The spleen filters the blood to remove old red blood cells. Remove this organ now.
7.
Carefully remove the entire digestive tract at this time. Be sure not to remove the kidneys. You will be removing the esophagus, the stomach, the small intestine, and the large intestine. Leave a few centimeters of the rectum. This whole tube in which food travels is known as the alimentary canal. Notice the cecum, small finger like projection where the small intestine and the large intestine meet. This functions to digest plant material.
8.
Describe the contents of the stomach, small intestine and large intestine.________________________________________________________________
________________________________________________________________________
________________________________________________________________________

Rat Dissection
1.
Extend the incision around both sides of the urogenital opening down to the anus. You may need to make lateral incisions further down to open up the urogenital system as shown in the following diagrams. Depending on the sex of your specimen, either use figure six or seven to identify the following organs.
Figure 6 Male urogenital system. To expose the entirety of the male reproductive system, the pubic bone must separated down the middle and the scrotum must be cut open from the ventral surface. Once the pubic bone has been severd at the pubic symphysis, the legs shoud be separated and bent back dorasally to view the reproductive system.
Figure 7 Female urogenital system (Notice the bifurcated uterus of the rat… this is different from humans that have a single medially located uterus)
Much of the urogenital system is surrounded by fatty tissue. Use your forceps to carefully uncover the kidneys and be very careful not to damage the ureters that bring urine from the kidney to the bladder.

Draw and label your rat’s urogenital system.
2.
What are the functions of: a.
Kidney- b.
Ureters- c.
Urethra- d.
Urinary bladder- e.
Ovaries- f.
Oviduct- g.
Uterus- h.
Vagina- i.
Scrotum- j.
Testes
Place your pig into plastic bag and seal. Place removed parts in a separate smaller bag. Place dissecting tools, sharp end down into cleaning solution. With soap and water clean the dissection tray.
Day 1
Surgeon_________________
Asst. Surg._______________
Day 2
Surgeon_________________
Asst. Surg._______________
Day 3
Surgeon_________________
Asst. Surg._______________
Reader__________________
Recorder________________
Reader__________________
Recorder________________
Reader__________________
Recorder________________