The fourth ventricle is a tent-shaped, fluid-filled space in the hindbrain, with the pons and upper medulla in front of it and the cerebellum behind; cut across, it is diamond-shaped. [1][2]
The 3D brain needs JavaScript. The text below still says where the fourth ventricle is and what it does.
Slice
Opens cut by a side (sagittal) slice through the fourth ventricle. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
It runs from the cerebral aqueduct at the top down to the obex in the lower medulla, where it narrows into the central canal of the spinal cord; the obex lies at the level of the foramen magnum. [1][2]
Its floor, the rhomboid fossa, is the back surface of the pons and upper medulla; a median sulcus divides it into left and right halves. [1][2]
Its roof faces the cerebellum: the superior medullary velum above, the inferior medullary velum and tela choroidea below; its side walls are the cerebellar peduncles. [1]
What it does
It is the link between the ventricular system, where cerebrospinal fluid is made, and the subarachnoid space, where it is absorbed; choroid plexus in its lower roof adds fluid too. [1][3]
Bulges in its floor mark nuclei underneath: the facial colliculus, where the facial nerve loops round the abducens nucleus, and the hypoglossal and vagal trigones over the hypoglossal nucleus and the dorsal nucleus of the vagus nerve. [1]
Connections
Fluid enters at the top through the cerebral aqueduct, which runs down through the midbrain from the third ventricle. [1][4]
It leaves through three openings in the lower roof into the cisterna magna, part of the subarachnoid space: a single median aperture and two lateral apertures at the lateral recesses. [1][2]
At its lower tip it continues as the central canal of the spinal cord. [2][5]
Other names
Its floor is called the rhomboid fossa, after its diamond shape. The median aperture is also called the foramen of Magendie, after François Magendie, who described it. [1][6]
Size
On this model the fourth ventricle measures about 23 mm front to back, 38 mm top to bottom and 28 mm side to side (the box it fits in, not its volume). [7]
Centre of the fourth ventricle compared with the centre of the pons: 16 mm further back, 8 mm lower; 18 mm apart in a straight line. [7]
Centre of the fourth ventricle compared with the centre of the cerebellum: 20 mm further forward, 3 mm lower; 21 mm apart in a straight line. [7]
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.