8Part I. External Anatomy Pre-Dissection Questions:Where do rats live?Would you typically see a rat during the day or night?What do rats eat?Do rats give birth to live young?What scientific term means to give birth to live young?
9External Anatomy - Teeth All mammals have teeth that correspond to the type of food they eat.The name RODENTIA comes from the Latin word meaning “to gnaw”. Rodents such as the rat have 2 pairs of CONTINUOUSLY GROWING INCISORS (front teeth) which are kept at the correct length by constant chewing.
10The mouth of the rat has a large cleft in the upper lip which exposes the large front INCISORS – locate them.How long are they? Are they easily seen? Describe them compared to the other teeth.
11External Anatomy – Cranial Region Notice the rat has a hairy coat that covers the entire body and sensory whiskers located on the rat’s face.VIBRISSAE (whiskers) enable rats to feel their way through tight spaces in the dark.Describe these whiskers:
12External Anatomy – Cranial Region Locate the EYES with the large pupil and the nictitating membrane found at the inside corner of the eye.This membrane can be drawn across the eye for protections similar to eyelids found in humans.What color eyes does your rat have?
13External Anatomy – Cranial Region Locate the external EARS in rats are surrounded by a PINNA, which is a flap of cartilage covered by skin that can rotate to direction of sounds heard by the ears.Locate the external NARES used for respiration and odor detection.
14External Anatomy – Abdominal Region Locate the TEATS (nipples) on the ventral (stomach) side of the rat.Regardless if your rat is male or female – does your rat have teats? ___________Remember a mammal, male or female will have mammary glands, nipples.
15External Anatomy – Pelvic Region Locate the exit openings for the digestive, excretory, and reproductive body systems.Like humans, male rats have 2 exit openings; females have 3 exit openings.In addition, females have a separate opening for reproduction and excretory waste (urine).Males have a SHARED urogenital opening that releases both sperm and urine.
17What Sex Is It?Because mammals are endothermic animals creating lots of internal heat, and the ideal temperature necessary for sperm production is a few degrees cooler than body temperature, male mammals, must have their TESTES suspended outside their bodies in a sac (SCROTUM) to keep them cooler.Testes outside the body in a scrotum are called TESTICLES.Is your rat male or female? _____________
18External Anatomy - Tail Examine the TAIL of your rat.What are some observations about the tail of your rat?Rats do not have hair on their tails unlike many other rodents that do like, gerbils, squirrels, and chipmunks.
19Part II: Dissection Preparation Exposing the Abdominal & Thoracic Cavities
20STEP ONE – SKIN LAYERYou will need to separate the skin from muscles for your first cuts similar to the fish and amphibian dissections.This time – START AT THE NECK AREA. There should be an incision hole that you can use to begin.You will need to use your metal blunt ended probe to separate the connective tissue of the skin from the first layer of muscle. When you have gotten a section separated you can begin to cut carefully down towards the anus.YOU MUST CONTINUE USING THE PROBE TO TEASE AWAY THE SKIN FROM THE MUSCLE AS YOU CUT TO PREVENT CUTTING THE MUSCLE TISSUE! GO SLOWLY! DO NOT CUT THE MUSCLES!
24STEP TWO – CUTTING THROUGH MUSCLES Mammals are known as EUCOELOMATES. There is a space you see surrounding the internal organs that is called the “true coelom” – the body cavity is lined with a membrane.Mammals have a DIAPHRAGM.This is a sheet of muscle that separates the body cavity into two compartments:Thoracic Cavity – heart and lungsAbdominal Cavity – digestive, excretory, and reproductive organsFor this reason the rat must be dissected in TWO STAGES!
25DIGESTIVE SYSTEM DISSECTION Use your scissors to cut through the abdominal wall of the rat following the incision marks in the picture provided.Be careful not to cut too deeply and keep the tip of your scissors always points upwards.Start at the lower abdomen and cut up towards the diaphragm.To locate the diaphragm feels where the ribs are located and it will be just next to them.Then make two incisions towards the back of the rat like you see on your picture.
26Abdomen cuts ONLYBe careful!Stop when get to the diaphragm!