MINK DISSECTION

OBJECTIVES:

During this activity, you will observe and dissect a mink to develop a better understanding of mammalian anatomy. This mink is an excellent organism for dissection purposes due to its size, availability, and similarity to humans.

BACKGROUND:

The American mink, Neovisionvision, is an agile, semiaquatic member of the family Mustelidae, which includes weasels, otters, and ferrets. Like most members of this family, mink have a slender body with short legs and a long, thick tail. Typical mink have soft, thick, dark brown fur, and are covered with protective oily guard hairs. Their slightly webbed feet make them excellent swimmers. Mink are found throughout North America and typically live in wooded areas near streams, rivers, lakes, or ponds and marshes. Members of the order Carnivora, mink prey upon muskrats, mice, snakes, frogs, and birds. They are important in regulating the freshwater food chain. While they have few natural enemies, bobcats or coyotes sometimes kill mink. Humans are their greatest threat. They are targeted by humans over trapping when fur prices are high (most minks for fur are raised onfur farms).

Mink are territorial. Like other animal in the weasel family, they use a musky and foul-smelling secretion from anal glands to mark their boundaries. The odor is considered by many to be as irritating as that of skunks. These pheromones are not only useful for marking boundaries; they also play a role in defense, courtship behavior, and recognition within a mink population.

PART 1: CLASSROOM RULES

  1. No food or drink in the lab.
  2. Dress appropriately. No open toe shoes!
  3. Wash & dry the equipment you used during the dissection. Wash & dry your table at the end of the period.
  4. DO NOT touch specimen and then touch face, eyes, etc.
  5. Report any unusual reaction (burning eyes, nausea, skin irritation to the teacher IMMEDIATELY!)
  6. When using the scalpel or scissors- YOU MUST CUT AWAY FROM YOURSELF AND OTHERS!! You will be shown the proper method to hold and dissect with the probe.
  7. All sharp utensils must be stored under the BLUE MAT.
  8. Appropriate behavior must be obeyed at all times during the lab. Any fooling around, walking around or mistreatment of the specimen will result in an immediate failure and removal from class. THIS IS YOUR WARNING!
  9. When pointing to a structure, you must always use a probe.
  10. When using blunt end scissors, the blunt end touches the tissue.

PART 2: LAB GROUP JOB DESCRIPTION

Reader (1)

Reads the lab procedure.

Makes sure group members are following along and on task.

Assists other group members.

Equipment Manager (1 or 2)

Gets the equipment from the supply area.

Inventories and inspects the lab equipment.

Washes and dries the lab equipment at the end of the lab period.

Dissectors

Performs the actual dissection.

Must wear gloves.

Prepares the mink for storage.

PART 3: EQUIPMENT AND MATERIALS

DISSECTING Tools

  • 1 pair of scissors (left open when not in use)
  • 1 pair of forceps
  • 1sharp probes
  • 1 blunt probes
  • 1 Scalpel

PART 4: GENERAL PROCEDURES

Lab Preparation (Beginning of the Period)

Obtain equipment.

Obtain a dissecting tray

Get your mink from Ms. Sacco/Clarke. Make sure you weargloves.

Remove the plastic bags from your mink.

Place the mink on the dissecting tray. You are ready to start the lab.

Clean Up - Mink

Take the mink to the trash can and discard without making a mess.

Clean dissection tray with soap and water. DRY the tray.

Clean Up – The Equipment

Wash the equipment with soap and water. Completely dry the equipment.

Turn your equipment into Ms. Sacco/Clarke.

Wash your table with soap and water. Completely dry your table.

PART 5: MINK DISSECTION—EXTERNAL ANATOMY

All of the associated questions or drawings can be found in your PAK. Complete as you go along in your dissection.

  1. The mink is a member of Class Mammalia and Order Carnivora. Examine your specimen carefully. What characteristics or features are observed that help place the mink in these taxa? Record your observations in your PAK work.
  2. Note the sensory organs concentrated around the head. The pinnae (ears), nares (nostrils), and eyes will be easy to observe, although the vibrissae (whiskers) have probably been removed from the specimen.
  3. Examine the eyes more closely. Note the presence of a third eyelid, the nictitating membrane. This membrane moves laterally to cover the eye when the animal swims underwater. Another interesting feature of the eye is thetapetumlucidum, a reflective layer of tissue in the retina.
  4. Make sure that you observe a mink of the opposite sex, and compare male and female specimens. Note that both sexes have many of the same structures. For instance, there are eight mammae on the ventral surface (these may have been damaged or removed in the skinning process). In females, these structures are the opening to the mammary glands, which secrete milk for the young; in males, they have no known function. Also, both male and females have an anus located just ventral to the tail. Indigestible foodstuffs are eliminated from the body through the anus. Finally, feature common to members of the weasel family is the presence of analglands. Similar to a skunk’s spray, the mink’s anal secretions are considered repulsive and irritating to many. Note: If the anal glands are present. Do not puncture or damage these organs.
  5. Look closely at your specimen. Females have an external vestibule ventral to the anus. This reproductive opening also serves as a channel for release of urine from the body. The male mink’s penis is considered quite long in relation to the rest of the body. The length of the organ allows sperm to be deposited close to the eggs. Male mink also have a scrotal sac with enclosed testes near the anus. These structures may have been removed during skinning.

PART 6: MINK DISSECTION – NECK & THORACIC CAVITY

Neck

Begin by cutting and separating the sternomastoid muscles in the neck. Be carefulnot to go too deep. Locate the trachea. It is a tube that runs from the larynx tothe lungs. The trachea is held open by a series of cartilaginous rings in the wall.You can feel the cartilage rings when you run your finger along the trachea. Exposethe entire length of the trachea. The swollen area at the anterior end of thetrachea is the larynx. The larynx is formed by several cartilages and contains thevocal cords.

The esophagus is a collapsed tube located on the dorsal surface of trachea.Locate the esophagus and dissect it away from the trachea.

Thoracic Cavity

Use Diagram #2 to help you identify the structures in this section. Open thethoracic cavity by cutting through the muscles and rib cartilages on the left side ofand parallel to the sternum. Keep the scissors pointed ventrally (toward you) asmuch as possible to avoid damaging structures in the cavity. Pull the walls of thecavity lateral breaking the ribs. The thymus gland is a mass of dark brown tissueembedded in the fat cranial to heart. Carefully remove the thymus and fat fromaround the major organs. Use a probe and forceps instead of a scalpel. Take careto avoid damaging the blood vessels.

The heart lies in the pericardial cavity, delineated by the tough pericardium.The lungs lie in the pleural cavities, the other subdivisions of the thoracic cavity.The right lung has three major lobes, the apical, cardiac, and diaphragmatic,and a fourth smaller intermediate lobe, more dorsal in position and associatedwith the postcava. The left lung has two lobes, the apical and diaphragmatic.Follow the trachea and esophagus as they enter the thorax. Dorsal to the heart,the trachea divides into left and right bronchi, which carry air to and from thelungs. Defer dissection of this region until after removal of the heart in Part II.

The esophagus continues dorsal to the heart and penetrates the musculardiaphragm to enter the abdominal cavity. The periodic contractions of thediaphragm, together with the forward and outward movement of the ribs, increasethe volume of the pleural cavities and cause inspiration of air into the lungs.

DIAGRAM 2: VISCERA OF THE THORAX

  1. Be sure you can identify the following parts:

Trachea Right lung, apical lobe

Larynx Right lung, cardiac lobe

Esophagus Right lung, diaphragmatic lobe

Thymus gland Right lung, intermediate lobe

Heart Left lung, apical lobe

Pericardium Left lung, diaphragmatic lobe

Bronchi Diaphragm

PART 7: MINK DISSECTION – ABDOMINAL CAVITY

Use Diagrams 3, 4 and 5 to help you identify the structures in this section. Open the abdominal cavity by making a single incision through the ventral body wall from the end of the sternum to the pubis. Cut the body wall also along the edges of the rib cage and reflect the muscle sheets laterally to expose the viscera.

DIAGRAM 3: VISCERA OF THE ABDOMEN DIAGRAM 4: STOMACH

Anteriorly, the dark lobes of the liver should be visible. The mesentery between the liver and the diaphragm is the falciform ligament. It divides the liver into right and left sides. The lobe of the right side of the liver closest to the midline (the right median lobe) contains the dark green gall bladder. You may need to lift the right median lobe of the liver and look under it in order to see the gall bladder. You may need to cut and remove part of the right median lobe to see the gall bladder

Identify the stomach. The stomach is attached to the liver and part of the small intestine by a mesentery called the lesser omentum.

Attached to the greater curvature of the stomach is the greater omentum, an extensive sheet of mesentery laden with fat. It extends caudally and covers most of the remaining abdominal viscera. Cut the greater omentum near its attachment to the stomach and remove it. Try to keep all the other mesenteries intact. Identify the regions and parts of the stomach and cut it open to expose its inner surface. Note the gastric rugae, the large longitudinal ridges. Size of the stomach in the mink, as in other carnivores, depends on how recently and how well the individual ate. If the stomach in your animal is full of food, it may be enormous. The stomach is closed by contraction of the pyloric sphincter. When the sphincter relaxes, food is permitted to pass into the small intestine.

The spleen is a greenish-brown organ lying in a mesentery on the left side of the stomach. Locate the spleen.

DIAGRAM 5: VISCERA OF THE ABDOMEN

Identify the small intestine, which begins at the pyloric sphincter. In the mesentery of the first part of the small intestine lies the right limb of the pancreas. It is pinkish (brown in some minks) and rather loose in structure. Theleft limb lies near the stomach and extends to the spleen. The products of thepancreas (digestive enzymes) and of the liver (bile) are carried into the smallintestine by a common duct system. Find the large cystic duct from the gallbladder and several hepatic ducts from the liver. These join to form the commonbile duct. Bile passes from the liver to the gall bladder, where it is stored andconcentrated. Eventually it is emptied into the small intestine. The common bileduct enters the small intestine near the pylorus, and its point of entry may bemarked internally by a small papilla. The two pancreatic ducts, one form eachlimb, join the common bile duct just before it enters the small intestine.Occasionally one of the pancreatic ducts will have a separate entry to the intestine.

The small intestine is divided into three segments: the duodenum, which begins atthe pyloric sphincter, the jejunum, and the ileum. Identify the duodenumattached to the stomach. Identifying the jejunum and the ileum require histological(tissue) study. The ileum opens into the large intestine, or colon. There is nocecum, or pouch, developed at this point in the gut of the mink. The colon is notdivisible into ascending, transverse, and descending segments as in many othermammals. It is instead a short descending tube that ends in the rectum.

The mink has a pair of anal glands associated with the rectum. They produce evil-smellingmusk and are usually removed during commercial preparation of dissectionspecimens. If they have not been removed, don't break them open!!

  1. Be sure you can identify the following parts:

Diaphragm Intestines

Liver Duodenum

Gall bladder Pancreas

Stomach Cystic duct

Greater omentumRectum

Gastric rugaeSpleen

Pyloric sphincterDiaphragm

PART 8: MINK DISSECTION – HEART

The circulatory system of the mink consists of lymphatic ducts and the bloodvascular system (heart, arteries, veins, portal veins, and capillaries). The arteriesand veins of your specimen should be injected with colored latex -- red for systemicarteries and blue for systemic veins. The hepatic portal system, if injected, shouldbe yellow. If it is not injected, the vessels can be traced because the dark browncoagulated blood is visible through the thin walls. Use forceps and a blunt orflexible probe when tracing vessels.

Arteries carry blood from the heart to capillary beds in either the lungs or the restof the body. Arterial blood is under high pressure, and the walls of arteries arethick. Veins carry blood from capillary beds back to the heart. Venous blood isunder low pressure, and the walls of veins are thin. Portal veins carry blood fromone capillary bed to another without passing through the heart.

Use Diagrams 6 and 7 to help you identify the structures in this section. Cut thepericardium and open the pericardial cavity. Note that the pericardium extendsonto the great vessels connected to the heart and is reflected back on them and onthe heart surface as the epicardium, or visceral pericarium. Cut the systemicaorta, the precava, the azygos vein, and the postcava. Refer to Drawings 2 and 3to help you identify the blood vessels. Gently lift the heart outwards and cut thepulmonary arteries and veins as close to the lungs as possible. The heart can thenbe removed from the body. Remove the excess fat from the epicardium.

The atria lie towards the right side of the chest. The ventricles are drawn to apoint, the apex, on the left side. Identify the left and right atria. The atria areseparated externally from the ventricles by the deep coronary sulcus. Right andleft ventricles are separated externally by a shallow interventricular sulcus in themusculature. Identify the stumps of all blood vessels leading to and from theheart.

The heart musculature has its own blood supply, the coronary arteries. Thesearteries come off the systemic aorta and run in the coronary sulcus. Branches runfrom the sulcus to the atria and down the ventricles to the apex, supplying themuscular heart wall. The heart muscle capillaries are drained by a number ofcardiac veins. Those draining the ventricular wall run from the apex toward theatria and empty into the coronary sinus on the dorsal surface of the heart. Thecoronary sinus empties into the right atrium.

Diagram 6: Heart, Ventral View

Diagram 7: Heart, Dorsal View

Place the heart between your fingers with the apex pointing up and the dorsal and ventral surfaces touching your fingers. Keeping this orientation put the base of the heart (atria side) down on the dissecting tray. With your scalpel, section the heart by cutting lengthwise, between your fingers, from the apex to the base of the heart. Remove the coagulated blood and latex from the heart and wash out the cavities. Be especially careful around the valves. Identify the right and left atria, right and left ventricles, bicuspid and tricuspid valves, precava, postcava,aortic arch, pulmonary trunk, and pulmonary veins. Note the chordatetendinaeand the papillary muscles. Note that the wall of the atrium is much thinner than the wall of the ventricle.

  1. Be sure you can identify the following parts:

External ViewInternal ViewAttached Blood Vessels

R. atrium R. atrium Precava

L. atrium L. atrium Post cava

R. ventricle R. ventricle Aortic arch

L. ventricle L. ventricle Pulmonary trunk

Coronary arteries Pulmonary veins

Cardiac veins

PART 9: MINK DISSECTION – ARTERIES & VEINS

Use Diagrams 8, 9, 10 and 11 to help you identify the blood vessels. Clean thevessels in the thoracic cavity. The systemic aorta curves dorsal as the aortic archand then runs caudal as the thoracic aorta. Two major arterial trunks come offthe arch of the aorta, the brachiocephalic and the left subclavian. Thebrachiocephalic gives off the right internal thoracic artery to the ventral chestand then divides into its three major branches, the left and right commoncarotids and the right subclavian artery.