Corpora Quadrigemina Sheep Brain

1. Obtain a preserved sheep brain and rinse it thoroughly in water to remove as much of the preserving fluid as possible.

2. Examine the surface of the brain for the presence of meninges. (The outermost layers of these membranes may have been lost during removal of the brain from the cranial cavity.) If meninges are present, locate the following:

dura mater—the thick, opaque outer layer arachnoid mater—the delicate, transparent middle layer that is attached to the undersurface of the dura mater pia mater—the thin, vascular layer that adheres to the surface of the brain (should be present)

3. Remove any remaining dura mater by pulling it gently from the surface of the brain.

4. Position the brain with its ventral surface down in the dissecting tray. Study figure 30.1 and locate the following structures on the specimen:

cerebral hemispheres convolutions (gyri)

sulci longitudinal fissure frontal lobe parietal lobe temporal lobe occipital lobe cerebellum medulla oblongata

5. Gently separate the cerebral hemispheres along the longitudinal fissure and expose the transverse band of white fibers within the fissure that connects the hemispheres. This band is the corpus callosum.

6. Bend the cerebellum and medulla oblongata slightly downward and away from the cerebrum (fig. 30.2). This will expose the pineal gland in the upper midline and the corpora quadrigemina, which consists of four rounded structures associated with the midbrain.

Figure 30.1 Dorsal surface of the sheep brain.

Sulcus

Convolution (gyrus)

Cerebral hemisphere

Sulcus

Convolution (gyrus)

Cerebellum

Frontal Lobe Missing

Frontal lobe

Parietal lobe

Temporal lobe Longitudinal fissure Occipital lobe

Medulla oblongata

Frontal lobe

Parietal lobe

Temporal lobe Longitudinal fissure Occipital lobe

Cerebellum

Medulla oblongata

7. Position the brain with its ventral surface upward. Study figures 30.3 and 30.4, and locate the following structures on the specimen:

longitudinal fissure olfactory bulbs optic nerves optic chiasma optic tract mammillary bodies infundibulum (pituitary stalk)

midbrain pons

8. Although some of the cranial nerves may be missing or are quite small and difficult to find, locate as many of the following as possible using figures 30.3 and 30.4 as references:

oculomotor nerves trochlear nerves trigeminal nerves abducens nerves facial nerves vestibulocochlear nerves glossopharyngeal nerves vagus nerves accessory nerves hypoglossal nerves

9. Using a long, sharp knife, cut the sheep brain along the midline to produce a midsagittal section. Study figures 30.5 and 30.6 and locate the following structures on the specimen:

cerebrum cerebral hemisphere cerebral cortex white matter gray matter olfactory bulb corpus callosum

Figure 30.2 Gently bend the cerebellum and medulla oblongata away from the cerebellum to expose the pineal gland and the corpora quadrigemina.

Figure 30.2 Gently bend the cerebellum and medulla oblongata away from the cerebellum to expose the pineal gland and the corpora quadrigemina.

Infundibulum Pitutiary Gland

cerebellum white matter gray matter third ventricle fourth ventricle diencephalon optic chiasma infundibulum pituitary gland (this structure may be missing)

mammillary bodies thalamus hypothalamus pineal gland midbrain corpora quadrigemina cerebral peduncles pons medulla oblongata

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • maria grazia piccio
    What is the difference between the corpora quadrigemina of the human and sheep?
    2 years ago
  • Amethyst
    What is the function of the corpus quadrigemina?
    11 months ago

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