On the Cutting Edge: Exploring Sheep Organs
Sheep organ dissection offers an excellent opportunity for students to learn about anatomical structures and functions. It also allows students to explore the physiological links between organ systems and identify the general structures representative of mammals. Extending this activity to comparative dissection leads to an understanding of how organs differ among mammals, including humans. Use the following procedures to guide your students through dissecting the sheep brain, eye, and heart. Note: Put on an apron or lab coat, eye protection, and gloves before proceeding with dissections.
Sheep brain dissection
- Place the brain on a dissecting tray, dorsal side up. (see Fig. 1)
- Observe the dura mater, or outer meninges, if they are present and were not removed prior to preservation. The 2 remaining meninges, pia and arachnoid, form a thin covering that adheres to the cerebrum. Use forceps to gently remove them.
- Identify the cerebrum. On the cerebral surface, observe the grooves known as sulci. Also observe the ridges called gyri. Identify the medial longitudinal fissure, which separates the right and left hemispheres of the cerebral cortex.
- Locate the cerebrum’s 4 lobes. At the anterior portion of the brain is the frontal lobe, which controls motor functions. Dorsal to this lobe is the parietal lobe, which receives and processes somatic sensory information. Inferior to the parietal lobe are the temporal lobes. The temporal lobes receive and process auditory sensations. The dorsal portion of the cerebrum makes up the occipital lobe, which receives and processes visual sensations.
- Continue to explore the sheep brain and identify each of its parts, using the diagram (Fig. 2) as needed
|Figure 1||Figure 2|
Sheep eye dissection
- Observe the eye’s outer structure and identify the optic nerve, sclera, and cornea. Next, trim away the excess tissue on the sclera surrounding the eye.
- Hold the eye gently with your thumb at the cornea and your forefinger near the optic nerve. Begin a cross-section of the eye by making an incision slightly behind the middle of the eye through the sclera.
- Separate the eye into halves after you have completed the cross-section. Let the vitreous humor—gelatinous, transparent material found inside the eye behind the lens—and any associated structures slowly slide out of the eye. You may need to tease the vitreous humor gently away from the eye’s lining.
- Look at the inside front portion of the eye. The lens may still be suspended in the middle of the pupil. Tip the front portion over and let the lens and associated structures fall out.
- Observe the vitreous body, lens, and associated structures. The hyaloid fossa is an indention in the center of the vitreous body that supports the lens. Surrounding the hyaloid fossa is the zonula ciliaris, made up of suspensory ligaments that suspend the lens and stretch it to focus. You will also notice dark lines around the hyaloid fossa. These lines are pigment from the iris.
- Continue to explore the sheep eye and identify each of its parts, using the diagram (Fig. 3) as needed.
Sheep heart dissection
- Identify the heart’s base and apex. At the base are 2 earlike auricles, which are the 2 atria. The 2 ventricles make up the rest of the heart.
- Identify the right and left ventricles by gently squeezing the chambers on each side of the heart. The right ventricle has thinner walls and compresses more easily than the left, which has thick muscular walls because it pumps blood to the systemic circuit.
- Cut through the right atrium wall and remove a portion of it. Be careful not to cut the right ventricle. Observe the tricuspid valve. Use a probe to push through the valve’s opening and into the right ventricle. Observe the number of flaps, or cusps, that make up this valve.
- Make an incision through the right ventricle and remove the front portion of the wall. Locate the aorta. This vessel has a larger diameter than the pulmonary trunk and will branch immediately after leaving the left ventricle. Cut through the wall of the aorta until you see the aortic semilunar valve, which prevents blood from entering the left ventricle.
- Continue to explore the sheep heart and identify each of its parts, using the diagram (Fig. 4) as needed.
Carolina's Perfect Solution® Sheep Organs
You and your students deserve the very best quality and safest preserved organs available. With that objective in mind, Carolina scientists and technicians developed Carolina’s Perfect Solution®, a preservation formula that produces superior specimens while also improving the safety of your classroom or lab. Our proprietary formula ensures that organs are:
- SAFE for you, your students, and the environment
- CONVENIENT to use and easy to dispose of
- SUPERIOR in tissue texture and color
All sheep organs come with a complimentary dissection guide that includes more detailed dissection instructions, a glossary, and labeled diagrams of the specific organ. To learn more about our extensive selection of classroom dissection kits and resources and Carolina’s Perfect Solution® specimens, visit www.carolina.com/preserved, where you can also find secure online shopping, product information, classroom resources, activities, and additional teaching tips.