Hippocampal commissure

The lateral portions of the body of the fornix are joined by a thin triangular lamina, named the psalterium (lyra).

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

The terminal lamina creates the commissure plate.

This structure gives existence to the corpus callosum, the septum pellucidum, and the fornix.

The fornix splits into two columns at the front (anterior pillars), and then splits into two posterior crura.

These two crura are joined together through the hippocampal commissure.

The beginning of the splitting is called the psalterium or Lyra Davidis.

The latter name is used because the structure resembles a lyra (or triangular harp):

The two crura are the "chassis" of the lyra, and the commissure connections are the fibers.