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This manual is designed to guide you through the dissection of the brain of a sheep.  After following the guide, you will better appreciate the three-dimensional nature of the mammalian central nervous system (CNS).  We use a sheep's  brain for several reasons: 1) the sheep's brain is sufficiently high on the phylogenetic scale to possess those characteristics which make moving either up or down the scale (for comparisons sake) a relatively simple matter; 2)   the sheep's brain is large enough to allow most of the features in which we are interested to be seen with the unaided eye; and  3) sheep brains are readily available at a minimal cost as a by-product of the meat industry.

Hints for navigating through the guide.

 In order to discuss the brain,  it is necessary to use terms that are as unambiguous as possible.   Look at the following figures that contain the descriptive terminology for direction in both quadrupeds (four-footed animals) and  bipeds.  Distinguishing between these two classes of organisms is necessary because in the  biped the neuraxis (the axis of the CNS) makes nearly a  ninety-degree turn at the point at which the brain-stem merges with the spinal cord.  Spend some time studying these figures until the terms become automatic for you.

In addition to these terms concerning direction, we must also use nomenclature describing the planes of dissection. Use the following figure below to help you to learn these terms.

The final plane of dissection refers to the cuts made to the spinal cord. This plane of dissection is known as either a cross section or a transverse cut. Transverse cuts section the spinal cord as one would slice a salami.


There are two principal cells in the brain: neurons and glia. Neurons account for the two types of tissue that can be distinguished:  white matter and grey matter.  The appearance of white matter is due to the myelin sheath found on the axons of some neurons.  In contrast, cell bodies have no myelin sheath and as a result they look grey in color. 

White matter always refers to axons,which are also sometimes referred to as fibers or fiber bundles.   Here are some rules to remember about axons:

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