Bird Dissection Introduction: The bird is a vertebrate whose body plan is adapted to its requirements for flight. For example, the skeletal system is lightweight and very strong. The flight muscles of the chest may make up one fifth of the total mass of a birds’ body. Birds have extremely great energy requirements because of their high metabolic rate. The unique air sacs of their respiratory system provide them with a continuous supply of oxygen. In line with their needs for a streamlined, lightweight body, birds’ reproductive organs are small and inactive for most of the year. During the breeding season, however, the male and the female reproductive organs increase greatly in size. Objectives: To observe the external and internal anatomy of a bird. To determine the sex of a bird. To view the body systems: digestive, reproductive, muscular, skeletal, renal, respiratory, circulatory, nervous, and excretory Procedure: EXTERNAL ANATOMY 1. Obtain a preserved bird and place it laterally in a dissection tray. 2. Draw and label the following structures on the external feature of the bird: beak, cere, eye, ear, primary wings, hallux, tarsus. This is Figure 1. 3. Measure the length, from beak to tip of tail feathers, in cm of the bird. Record on Table 1. 4. Position the bird ventral side up and spread out one wing so that the various types of feathers are visible. 5. Locate the primary feathers, which are attached to the bones of the “fingers” and the wrist. Find the shorter secondary feathers, which are attached to the ulna. Finally, identify the smaller scapular feathers, which grow from the shoulder. Primary, secondary, and scapular feathers are all flight feathers and are covered by small, shingled covert feathers. 6. Pull out one of the primary feathers and examine it with a dissection microscope. Locate the long, slender, hollow shaft. From the shaft, you will note the barbs that extend outward at an angle of about 45 degrees. With your fingers, gently pull apart the barbs. Notice that they are formed of still smaller barbules, interlocking hooks. 7. Draw the feather and label; shaft, barbs, and barbules. This is figure 2. 8. Examine the bird’s head. Look closely at the eye, with its moveable upper and lower lid. Gently pull the lids back so that you can see the nictating membrane in the corner of the eye. 9. Locate the beak. The beak has two parts, the maxillary and the mandible. The maxilla is the moveable bottom portion of the beak. A horny sheath that grows continuously and is worn down with use covers both parts of the beak. 10. At the upper end of the beak is a slit-like nasal opening. Just behind this opening, locate a white structure called the cere, which is at the juncture of the beak and the head. 11. Carefully open the bird’s beak and look inside the mouth. Are there any teeth? 12. Just below and slightly behind the eye, look for the external ear opening. MUSCLE EXAMINATION 13. Place the bird ventral side up in the dissection pan. Pin wings so that they are spread out and anywhere else that is needed. 14. With a pair of forceps, lift the skin at the opening just above the tail. Make a shallow cut through the lifted skin with your scissors. 15. Insert the scissors into the opening and cut through the skin along a midventral line, from the cloacal opening to just under the head. 16. Make 4 cuts laterally; two into the wing areas and two into the leg areas. Fold back the layers of skin so that you can look at the muscles. The cut will be in the shape of an “I.” 17. Locate the two large pectoralis muscles, which are attached to the keel. Carefully cut through the one layer of muscle and peel it back to show a second layer beneath it. The lower layer is called the pectoralis minor muscle. Both pectoralis muscles (major and minor) are the flight muscles. 18. Using your scissors carefully cut through the skin of the left leg. Gently pull the skin so that you can see the muscles of the leg. As you look at the muscles of the leg, locate the iliotibialis muscle, which is the broad, heavy muscle of the upper leg. 19. Identify the long gastrocnemius muscle of the lower leg. Using your probe, move aside the layers of muscle in the lower leg so the at you can see the fibula bone beneath the muscle. 20. Study the skin of the bird’s feet. Note its texture and the presence or absence of feathers. Look at the top of the birds’ toes. INTERNAL ANATOMY 21. Cut through the pectoralis muscles. Completely lay back the pectoral muscles so the keel is visible. Using scissors, cut through the keel just left of the midventral line. NOTE: It does not matter if you crack the keel. Your purpose is to reveal the internal organs. DIGESTIVE SYSTEM 22. Remove any connective tissue or fatty tissue that is still attached to the organs of the digestive system. 23. Draw the internal organs that are visible and label the following: esophagus, trachea, crop, liver, gizzard, pancreas, intestine, cloaca, testes, ovary, heart. This is Figure 3 24. Locate the thin-walled flabby tube or esophagus, in the neck of the bird. This tube is the first part of the digestive system that is visible to you. 25. The lower part of the esophagus widens into a large, hard object called the crop. 26. Below the crop is the true stomach, which has two parts. The upper part is called the proventriculus. In this part of the stomach, digestive enzymes are secreted. The lower part of the stomach is called the gizzard. 27. The gizzard has strong muscular walls that can churn up the food. The gizzard may contain small stones or pebbles to grind up the food. 28. Examine the lower end of the intestine. You should be able to find two sac-like caeca. The caeca are at the junction of the intestine and the rectum. 29. Locate the cloaca (another name for the anus) which is the common exit of the digestive tract, reproductive organs, and urinary organs. You may be able to find the ducts leading from the kidneys to the cloaca. RESPIRATORY SYSTEM & CIRCULATORY SYSTEM 30. Locate the trachea (windpipe) in the throat region, which is ventral to the esophagus, except where the crop bulges over it. Run your fingers over the surface of the trachea. You should be able to feel the tracheal rings, which provide form to the wall. 31. Trace the trachea down to its lower end, where there is a somewhat swollen chamber. This chamber, which includes specialized internal membranes, is called the syrinx. The syrinx, an organ found only in birds, is the organ from which birds produce their various calls and songs. 32. Trace the synrix down to its base, where it divides into two smaller tubes called bronchi. Each bronchus leads to a lung. The lungs are relatively small organs. 33. Look for two flattened structures pressed against the ribs and lying on either side of the vertebrate column. Unique to birds is a system of air sacs that extend out from the lungs. 34. Look for the bird’s heart in the center of its chest cavity. It will probably be about 3cm long. Look for the major vessels entering and leaving the heart. Trace the blood vessels that join the heart to the lungs. 35. Cut out the heart and cut the heart in half to see the two chambers. RENAL & URINARY SYSTEM 36. In your study of the digestive system, you probably came across the kidneys. Locate the dark, three-lobed kidneys. They are just below the lungs and fit into a depression in the dorsal wall of the bird. The bird has NO urinary bladder. REPRODUCTIVE SYSTEM 37. If you have a male bird, look for two white testes. The testes are ventral to the kidneys and may be slightly anterior to them. Locate the narrow sperm ducts that lead from the testes to the cloaca. 38. If you have a female bird, look for the ovary on the left side of the body. The ovary is in about the same position as the left testis would be. Locate the oviduct, which should open close to the ovary. Trace the oviduct down to the cloaca. 39. Record the gender of your bird on Table 1. 40. Observe any organs you would like under the dissection microscope. Data: Drawings that should be included in your lab report: Figure 1 – External Lateral View Figure 2 - Feather Figure 3 – Internal Ventral View Table 1 Length of bird in cm Sex of bird Name of your bird Analysis: 1. Does a bird have teeth? 2. What are the 3 parts that make up a feather? 3. Which type of feathers is used for flying? 4. What are the 2 parts of the stomach in a bird and what do they do? 5. How do birds sing and what is the name of the structure that makes it happen? 6. What organ in the excretory system do birds not have? 7. Give three reasons why birds’ bodies are adapted to its requirements for flight. Conclusion: Write 2-3 sentences explaining what you learned in this dissection. NO PERSONAL PRONOUNS!