The third ventricle is a narrow, slit-like fluid-filled space on the midline of the brain, between the left and right thalamus, with the hypothalamus forming its lower walls and floor. [1][2]
The 3D brain needs JavaScript. The text below still says where the third ventricle is and what it does.
Slice
Opens cut by a side (sagittal) slice through the third ventricle. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
It lies in the diencephalon, on the midline between the two lateral ventricles; it is narrow from side to side and roughly rectangular seen from the side. [1]
A groove on each side wall, the hypothalamic sulcus, separates the thalamus above and behind from the hypothalamus below and in front. [1]
In most brains the two thalami touch across it at the interthalamic adhesion (massa intermedia), which the ventricle surrounds. [2][1]
Its back wall carries the pineal gland; its front wall is the lamina terminalis; its floor dips into a funnel, the infundibulum, that leads down to the posterior pituitary. [1]
What it does
It passes cerebrospinal fluid from the lateral ventricles on to the cerebral aqueduct, and choroid plexus in its roof adds fluid of its own. [1][2]
Connections
At its upper front corner the two interventricular foramina bring in fluid from the left and right lateral ventricles. [1][3]
At its lower back corner it becomes the cerebral aqueduct (aqueduct of Sylvius), about 15 mm long, which carries the fluid through the midbrain to the fourth ventricle. [1][4]
Small recesses reach out from it: the optic recess above the optic chiasm, the infundibular recess into the pituitary stalk, and the suprapineal and pineal recesses at the back. [1]
Other names
It is the third because the two lateral ventricles were at one time called the first and second ventricles. [2]
Size
On this model the third ventricle measures about 40 mm front to back, 23 mm top to bottom and 8 mm side to side (the box it fits in, not its volume). [5]
Centre of the third ventricle compared with the centre of the left thalamus: 10 mm further forward, 3 mm lower, 13 mm closer to the midline; 16 mm apart in a straight line. [5]
Centre of the third ventricle compared with the centre of the fourth ventricle: 25 mm further forward, 43 mm higher; 50 mm apart in a straight line. [5]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.