实验白鼠,解剖 z-bo 2020-08-13 612

　　purpose

　　Learn how to dissect rats and mice, and understand the general characteristics of Mammalia and rodents.

　　Thinking before the experiment Rats and mice are both widely used experimental animals. Although they are small, they have all the characteristics of mammals. If you can compare on the basis of mastering the morphology and structure of rabbits, you can deepen your understanding of rodents.

　　Material equipment Rats, mice; wax trays, pins, dissectors, bone scissors, thin glass tubes, absorbent cotton;

　　Step

　　1. Dissecting a mouse

　　(1) Dissection method Put the mouse in a closed container, and then put in a cotton ball. After 3 to 5 minutes, the mouse has been anesthetized. Put the anesthetized mouse on the wax tray, pin the palms of its limbs with a pin, use a wet cotton ball to moisten the hair on the midline of the abdomen, lift the skin in front of the genitals, cut a small cut with scissors, and cut along the midline of the abdomen Under the jaw, separate the skin to the sides. Then cut the muscles of the lower abdomen, and cut the muscles along the midline to the lower edge of the sternum. After cutting the lower end of the rib to the left, cut forward and upward until the left clavicle is broken. After the same treatment on the right side, the front wall of the chest can be peeled off, and the left and right abdominal walls can be fixed with pins. This shows the natural arrangement of its internal organs. Observe the beating of the heart and the thin muscular diaphragm between the chest and abdomen and the peristalsis.

　　(2) Observe the mouse’s digestive system Use forceps to open the mouth, you can see: 4 incisors, 12 molars and tongue. Then use forceps to lift the trachea at the front of the neck, and you can see the muscular esophagus passing through the chest and the diaphragm, connecting the pocket-like stomach, under the stomach is the intestine, which is connected by the mesentery to the abdominal cavity. There is a yellow-green gallbladder inside the right liver, and a pink pancreas under the stomach. Use a scalpel to gently open the mesentery and straighten the intestine. There is a caecum at the junction of the slender small intestine and the stubby large intestine. An olive-shaped fecal mass can be seen in the large intestine.

　　(3) Observe that the nostril of the respiratory system of the mouse is the nasal cavity. There is a long tubular trachea at the front of the neck, supported by an incomplete cartilage ring. Touch with your fingers and feel elastic. The lower end of the trachea divides into two bronchi into the lungs. The lungs are rose-colored and spongy, with left and right leaves close to the ribs. Use a scalpel to make a longitudinal incision above the trachea, insert a thin glass tube, and blow inward to see the expansion of the lung lobes.

　　(4) The heart of the mouse is located in the middle of the left and right lung lobes. Carefully cut the heart capsule and see a conical heart. The upper part is two atria shaped like ears, and the lower part is the ventricle. If the mouse is lightly anesthetized, the atria and ventricles can be seen to contract alternately. Pinch the ventricle with your fingers and feel that the wall of the left ventricle is much thicker than the wall of the right ventricle.

　　(5) The clonal system of mice includes excretory organs and reproductive organs. Their excretory organs are behind the upper part of the abdominal cavity. There are a pair of purplish red broad bean-shaped kidneys on both sides of the spine. The right kidney is more advanced than the left kidney, and each has a ureteral bladder.

　　mice dioecious. In male mice, there are a pair of oval testicles on both sides of the bladder at the lower end of the abdomen (not visible during reproduction, it has fallen into the scrotum), and each testis is connected to a thin, difficult-to-see vas deferens. Female mice have a pair of small ovaries on the dorsal side of the abdominal cavity, which are often difficult to see, but the "V"-shaped fallopian tubes and uterus below it are clearly visible.

　　2. Dissecting a white rat

　　(1) The dissection method is the same as the treatment and dissection of the mice.

　　(2) Observe the digestive system of the rat. Use a scalpel to deeply cut the masseter muscle and cut the opening angle with bone scissors. Pull the mandible back forcefully to fully expose the mouth. You can observe that it has 4 chisel-shaped incisors and 3 left and right incisors. On the molars. Behind the base of the tongue is the pharynx, tapering downward. Lift the trachea with forceps and see that there is a fleshy esophagus at the back, connected to the pharynx at the top, and the cardia in the middle of the stomach at the bottom. The curvature of the stomach is not significant (remarkable in rabbits), there is a more developed two-layered pocket-like omentum in front of the stomach (rabbits are not developed), the stomach wall of the left cardia is thin, gray and translucent, and the wall of the right pylorus Thick, blood vessels are mostly red-gray. There is a striped spleen under the stomach.

　　The small intestine is divided into three parts: the duodenum, jejunum, and ileum. The pylorus of the stomach connects to the duodenum. It forms an incomplete ring and surrounds a part of the pancreas. In the front under the diaphragm, there is a dark red liver divided into 6 lobes. The common hepatic duct leads to the duodenum. The pancreas is a multi-branched light yellow gland with several pancreatic ducts, some of which enter the liver duct, and some directly enter the duodenum (a rabbit has a gallbladder, and only one pancreatic duct, which directly enters the duodenum). The jejunum and the ileum have little difference in appearance. They are coiled in the abdominal cavity. The cecum is the caecal sac at the junction of the small intestine and the large intestine. It is 6 to 8 cm in length (above 50 cm in rabbits). Tighten the bowel into a loop. It can be divided into ascending, transverse and descending colons, with a shorter rectum at the end.

　　(3) In the rat’s trachea and lung neck, under the thyroid cartilage and in front of the esophagus, the trachea supported by more than 20 incomplete cartilage rings enters the thoracic cavity and divides into the left and right branches into the lungs. The left lung has only one lobe and the right The lung is divided into four lobes, and the lung is a spongy organ. There are pink, butterfly-shaped thyroid glands on both sides and front of the trachea near the larynx.

　　(4) The clonal system of a white mouse, like that of a mouse, also includes two parts: urinary organs and reproductive organs. The urinary organs are a pair of dark red bean-shaped kidneys, which are recessed on the inside called the renal hilum, and each extends a white ureter into the bladder. The bladder is a retractable translucent sac that receives urine from a pair of ureters on both sides of its base. It passes into the urethra behind the base and leads out of the body. Its reproductive organs are male and female. First, roughly identify male and female in appearance. Three holes of anus, urethra and vulva can be clearly seen, and 6 pairs of nipples on the body surface are obviously female. The distance between the genital pore and the anus is relatively large, and only two pores are male. In males, the testicles are a pair of white beans that descend into the scrotum during the reproductive period and are not retracted into the abdominal cavity through the inguinal canal (that is, the murine tube) during the reproductive period. There is an epididymis at the end of the testis. Into the yin channel to the body, there is a pair of coronal seminal vesicle glands on the ventral surface at the junction of the vas deferens and the bladder. In females, the purple-yellow glands with granular protrusions above the kidneys are ovaries, each with a thin fallopian tube on the outside. There is a bell mouth near the ovary that opens into the abdominal cavity, and the uterus expands below the fallopian tube, and the uterus on both sides are combined into a "V" shape, each opening in the vagina and outside the body.

　　Analysis and discussion

　　1. Rabbits, rats, and mice are all representative mammalian experimental animals. Although the current middle school zoology uses rabbits as the representative animal, due to the source of materials and economic conditions, many schools use rats or mice as experimental materials. In terms of understanding the characteristics of Mammalia, the experimental results are the same. Of course, rats or mice are smaller, and their organs are not as clear as rabbits.

　　2. Rats and mice belong to the order Rodentia, and rabbits belong to the order Lagomorpha. Their food habits are different. Therefore, in terms of the digestive system, the two types of teeth, stomach, gallbladder, pancreatic duct, and cecum are different. The other systems are very similar. It is worth pointing out that the reproductive systems of the two are basically the same, but different from most other mammals. For example, the inguinal canal (mouse tube) of a male individual is open for life, so the testis only descends into the scrotum during the reproductive period. Females are typically double uterus, with both uterus opening independently from the vagina.