Superior colliculusOne of two bumps on the back of the midbrain. They are part of the tectum.
Cerebral aqueductThe narrow channel through the midbrain. Fluid passes along it to the fourth ventricle.
Periaqueductal grayA sleeve of gray matter around the cerebral aqueduct.
Tegmentum of the midbrainThe middle zone of the midbrain. It holds the red nuclei and runs on into the tegmentum of the pons.
Red nucleusA round nucleus in the tegmentum, one on each side. It shows in a cut at the superior colliculus.
Substantia nigraA band of pigmented cells in front of the tegmentum. It lies between the tegmentum and the crus cerebri.
Crus cerebriThe front part of each cerebral peduncle. Fibers from the cortex run down through it, among them the corticospinal tract.
Pons 6
Fourth ventricleThe fluid-filled space behind the pons. Its floor is the back of the pons and of the upper medulla.
Tegmentum of the ponsThe back part of the pons, under the fourth ventricle. It holds part of the reticular formation.
Basilar part of the ponsThe large front part of the pons. The pontine nuclei and the cross fibers lie in it.
Pontine nucleiSmall clusters of nerve cells in the basilar part. Their fibers cross the midline as the middle cerebellar peduncle.
Corticospinal fibersMotor fibers on their way from the cortex to the spinal cord. They run down through the basilar part to the pyramids.
Middle cerebellar peduncleA thick stalk from the pons to the cerebellum. There is one on each side, formed by fibers from the pontine nuclei.
Medulla 5
PyramidA bulge beside the front midline of the medulla. Motor fibers from the cortex run down in it.
Inferior olivary nucleusThe nucleus inside the olive. It makes the bulge on the side of the medulla.
Medial lemniscusA band of sensory fibers beside the midline, behind the pyramid. It carries fine touch and position sense upward.
Inferior cerebellar peduncleA stalk from the medulla to the cerebellum, one on each side. It lies beside the floor of the fourth ventricle.
Floor of the fourth ventricleThe back surface of the open medulla. Here the central canal has widened into the fourth ventricle.
How this list was compiled: Every name checked on 2026-10-01 in at least two of these. (1) Wikipedia, English edition, Midbrain, Pons, Medulla oblongata, Fourth ventricle and Corticospinal tract, https://en.wikipedia.org/wiki/Midbrain. (2) TeachMeAnatomy, The Midbrain, The Pons and The Medulla Oblongata, https://teachmeanatomy.info/neuroanatomy/brainstem/midbrain/. (3) Henry Gray, Anatomy of the Human Body, 20th edition (1918), https://archive.org/details/anatomyofhumanbo1918gray. Detail lines are in our own words. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
Three brain stem cross sections labeled part by part: the midbrain, the pons and the medulla oblongata. Each has the back of the brain stem at the top, and a small side view marks the level of the cut.
Read the full guide
Midbrain
Start at the top with the superior colliculi. The cerebral aqueduct is the slit in the round periaqueductal gray. Below come the tegmentum with the two red nuclei, the flecked substantia nigra and the crus cerebri.
Pons and medulla
In the pons the fourth ventricle is the space at the top and the tegmentum the slab under it. The large basilar part holds the pontine nuclei and the bundles of corticospinal fibers, and each arm is a middle cerebellar peduncle. In the medulla the strip along the top is the floor of the fourth ventricle, with an inferior cerebellar peduncle at each corner. The crinkled band is the inferior olivary nucleus; the medial lemniscus and the pyramids lie beside the midline.
Back to front in the midbrain: colliculi, aqueduct, tegmentum, substantia nigra, crus cerebri.
The same motor fibers pass through all three slices: crus cerebri, basilar part of the pons, pyramid.
Questions and answers
What does a cross section of the midbrain show?
From back to front: the two superior colliculi, the cerebral aqueduct inside the periaqueductal gray, the tegmentum with the red nuclei, the substantia nigra and the crus cerebri on each side.
What are the two parts of the pons in cross section?
The basilar part in front and the tegmentum behind. The basilar part holds the pontine nuclei, the cross fibers and the corticospinal fibers. The tegmentum lies under the fourth ventricle.
What makes the olive bulge on the side of the medulla?
The inferior olivary nucleus, which lies inside it. In a cut at this level it sits to the side of the pyramid and the medial lemniscus.
Which way up is a brain stem cross section drawn?
On this page the back of the brain stem is at the top and the front at the bottom. So the colliculi and the fourth ventricle are up, and the crus cerebri and the pyramids are down.