Fascinated by the rat in front of her, she hadn't realize there were instructions to the procedure. In movies, it always looked like it was a free-for-all, and the teenagers all tried varied methods of opening the dead animal. Willow with her latex gloves and protective glasses grabbed the rat. It fit in her hand. If it were alive, she could carry it outside and feed it baby carrots. However, due to the fact it was covered in a stinky liquid that reminded her of a morgue, she was reminded she was handling a dead animal she would need to open up. Zhi Yan noticed Willow's gaze on the laboratory rat, wondering what she was planning to do with it.
"Miss O'Neal, is everything okay?"
Raising her eyes to her teachers, Willow nodded. "I was just wondering in what they were kept in." Her nose wrinkled, "so that they don't rot off."
Zhi Yan smiled. She wondered if it came from a genuine interest from the girl, or a way to dodge a thorny situation. "It's formaldehyde. That's why it stinks." She paused then asked another question to the student. "Do you need help with the dissection? Are you feeling sick?"
Willow's eyes were back on the rat. She felt it in her hands. For some reasons, she wanted a pet rat now. "No, I'm fine," she raised her eyes back to her teacher, stating her honest opinion on the matter, "I think it's kinda cool."
She ended her statement early. At first, she wanted to say something like "it's kinda cool to see the inside of something that used to be alive" but she realized if someone overheard it, it might bring some negative attention. She put back the rat in the little tray it came with and looked at the her tools. There were needles, a scalpel, and a pair of pliers. Zhi Yan noticing that Willow finally put down the rat, felt like she could go back to her desk. She didn't like students picking up the dead animals with such interest, in the past someone ran home with one, and she didn't like receiving the phonecall that someone tried to bring back to life a frog.
Willow looked at her list of tasks.
Part 1: No dissection needed:
- Obtain rat.
- Place your rat in a dissecting tray and examine the external features. The rat (and all vertebrates) has anatomical regions to help locate structures.
- Locate the vibrissae (whiskers) and the pinna (ears). Rats are gnawing mammals and two large incisors should be visible. Eyes are usually pink or black with a black pupil and covered by a nictitating membrane.
Part 2: Dissection:
- Carefully remove the skin of the rat to expose the muscles below. This task is best accomplished with scissors and forceps where the skin is gently lifted and snipped away from the muscles. Start at the incision point where the latex was injected and continue toward the tail. Use the lines on the diagram to cut a similar pattern, avoiding the genital area. Gently peel the skin from the muscles, using scissors and a probe to tease away muscles that stick to the skin.
- Carefully tease away the biceps femoris and gastrocnemius to expose the 3 leg bones: Tibia, Fibula, and Femur
- Locate the liver, which is a dark colored organ suspended just under the diaphragm. It has four lobes:
median or cystic lobe - located at the top, there is an obvious central cleft
left lateral lobe - large and partially covered by the stomach
right lateral lobe - partially divided into an anterior and posterior lobule, hidden from view by the median lobe
caudate lobe - small and folds around the esophagus and the stomach, seen most easily when stomach is raised
- Find the stomach, its a curved organ lying just under the liver. At the top of the stomach you can see the esophagus where it pierces the diaphragm and joins the stomach. Lifting the stomach up may reveal a bumpy glandular organ: the pancreas.
- The spleen is about the same color as the liver and is attached to the greater curvature of the stomach.
- The small intestine is a slender coiled tube that receives partially digested food from the stomach (via the pyloric sphincter). It consists of three sections: duodenum, jejunum and ileum, (Listed in order from the stomach to the large intestine.) The duodenum is recognizable as the first stretch of the intestine leading from the stomach, it is mostly straight. The jejunum and ileum are both curly parts of the intestine, with the ileum being the last section before the small intestine becomes the large intestine.
- Locate the colon, which is the large greenish tube that extends from the small intestine and leads to the anus. The colon is also known as the large intestine and it consists of four sections:
cecum - large flattened sac in the lower third of the abdominal cavity, it is a dead-end pouch and is similar to the appendix in humans.
ascending colon – food travels upward.
transverse colon – a short section that is parallel to the diaphragm
descending colon – the section of the large intestine that travels back down toward the rectum.
rectum - the short, terminal section of the colon that leads to the anus. The rectum temporarily stores feces before they are expelled from the body.
- Please carefully clean your tray and refer to the teacher when you are done.
