hippocampal commissure

This lamina contains some transverse fibers that connect the two hippocampi across the middle line and constitute the commissure of fornix (hippocampal commissure).

There are also two much smaller connections, the anterior commissure and hippocampal commissure, as well as many subcortical connections that cross the midline.

In the rat, the two hippocampi resemble a pair of bananas, joined at the stems by the hippocampal commissure that crosses the midline under the anterior corpus callosum.

Smaller commissures also join the hemispheres, both in eutherian and in other vertebrates, including the anterior commissure (which is present in marsupials), posterior commissure, and hippocampal commissure.

The great majority of fibers connecting the two hemispheres travel through the corpus callosum, which is over 10 times larger than the anterior commissure, and other routes of communication pass through the hippocampal commissure or, indirectly, via subcortical connections.

The septum is continuous with the preoptic area across the plane defined by the anterior commissure; it is largely subpallial, but also contains a small pallial portion, where the hippocampal commissure forms, which is contiguous to the medial pallium.

These findings are consistent with anatomy and evolution; the anterior commissure (and the hippocampal commissure; see the figure on p. 167) lies deeper than the corpus callosum and transfers information in the limbic cortex and perhaps in other more ancient components of the brain.