Lab 2 - Internal Organization of the Brain

Fornix, Corpus Callosum, Anterior Commissure and Optic Fibers

First we will consider the fiber tracts: Fornix, Corpus Callosum, Anterior Commissure, and the Optic Chiasm. Next the cell bodies: Amygdala, Uncus and the Parahippocampal Gyrus. Finally, we will find the Lateral and Third Ventricles. Recall that fiber tracts appear darker than cell bodies in myelin stains. The following figures are all myelin stains.

The Fornix is a C-shaped structure that is a major input and output pathway of the hippocampus. It begins caudal to the hippocampus and arches superiorly close to the midline under the corpus callosum. It then turns inferiorly and posteriorly toward the hypothalamus.

Fornix, Corpus Callosum, Anterior Commissure, Optic FibersThe Corpus Callosum joins the two cerebral hemispheres.

At the level of the Internal Capsule Genu we find the Anterior Commissure, a band of fibers that crosses the midline. A large portion of the anterior commissure is responsible for interconnecting the middle and inferior temporal gyri. Notice the Horizontal section of the anterior commissure has a caudal curve. Use this information when you track the anterior commissure in the coronal sections.

At the same level, we find the Optic Chiasm. The chiasm is where the fibers of the optic nerve partially decussate to form the optic tracts. Caudal to this level, we see the Optic Tract.

Use the Figure 1 to get an understanding for the location of these structures.