lab - Anju Mathew BI 117 EXTERNAL ANATOMY/SKELETON LAB 2...

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Anju Mathew BI 117 EXTERNAL ANATOMY/SKELETON LAB: 2. Fetal pig dissection: Tie one front legs of the animal with a string that passes underneath the dissecting pan to the other leg. Then repeat this with the back legs. Insert one blade of scissors through the body wall on one side of the umbilical cord and cut posterior to the base of the leg. Continue cutting from the anterior end of this cut so that it resembles an upside-down U. The finished cut will be anterior to the navel and along each side of the navel. The flap of body wall that contains the navel can be folded posterior to reveal the internal organs of the abdomen. Extend a single cut along the midline of the ventral surface of the animal to about 2 cm. from the chin. Cut completely through the body wall in the abdominal area but keep the cut shallow in the neck region. A cut is made on the side of the animal from the point just posterior to the diaphragm dorsally. A similar cut is made on the other side. These two cuts will enable us to spread open the abdominal cavity. Inside we would find all of the organs, veins, arteries, nerves and muscle. Up in the neck area we would find the esophagus, trachea, larynx, bronchus, and lungs. As we move down, we would find the lungs, heart and diaphragm. Once past the diaphragm we find all of our organs such as the stomach, kidney, pancreas, liver,
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large and small intestine, gallbladder, pancreas, and spleen, Toward the bottom half of the animal we would find all of the reproductive system. Rat dissection: Secure your specimen ventral side up, with the legs spread laterally with thread or pins (thread under the pan works better, usually). Beginning at the opened skin of the throat, and cutting very shallowly (scissors work better than scalpels for this), make a medial ventral incision the length of the body, then lateral incisions at the collar bones, the posterior margin of the rib cage, and at the hips, cutting deep enough to reach the body cavities but not so deep as to damage the organs inside. Free the resulting flaps of tissue, gently disconnecting it from underlying tissue with a blunt probe or careful cutting. You can pin the flaps aside or completely remove them. Look in the abdominal cavity. The abdominal organs may still be covered with a membrane, the peritoneum, but this usually comes off with the overlying layers. Another membrane, the mesentery, surrounds and supports most of the digestive system and its related circulation. Abdominal organs include liver, stomach, pancreases, large and small intestine, gallbladder, kidney, and bladder.
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Frog dissection: Place a frog on a dissection tray. To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs. A male frog usually has thick pads on its "thumbs," which is one external difference between the sexes. Male frogs are also usually smaller than female frogs.
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