Mesencephalon [Midbrain]

The midbrain (or mesencephalon) is the most rostral part of the brainstem. It contains the aqueduc of mesencephalon, which connects the fourth ventricle of the rhombencephalon to the third ventricle of the diencephalon.

The midbrain is divided into two parts:

• Dorsal part = the tectum, dominated by gray matter, which includes the rostral and caudal colliculi as well as the tectal plate.

• Ventral part = the cerebral peduncle, composed of the tegmentum, substantia nigra, and cerebral crus.

The midbrain is involved in vision, hearing, motor control, sleep and wakefulness, alertness, as well as temperature regulation.

In equids, the midbrain is relatively longer and narrower than in other animals.