Midbrain, also called mesencephalon, is the narrow part of the brain that passes through the tentorial notch and connects the forebrain to the hindbrain.
Anatomically, the midbrain is divided into two halves, known as cerebral peduncles. Each peduncle is further divided into two parts by a band of gray matter called substantia nigra. The anterior part is called crus cerebri and the posterior part is called tegmentum.
The midbrain has a narrow cavity, known as the cerebral aqueduct. It is a part of the ventricular system of brain and connects the third ventricle to the fourth ventricle.
It is the part of midbrain that lies posterior to the cerebral aqueduct. It contains four small surface swellings; the two superior and two inferior colliculi.
It is a small glandular structure that lies between the superior colliculi. It is attached by a stalk to the posterior wall of the third ventricle.