Dr. Rati TandonJ.N.M.C.,AMU,

ALIGARH

tent-like cavity of hindbrain situated in the posterior cranial fossa. triangular outline in sagittal section and

appears rhomboidal in shape in horizontal section.

Behind the pons and the upper part of medulla oblongata.

in front of the cerebellum

Important features:

recesses, angles,

boundaries, choroid plexus.

RECESSES Five in number:Two lateral

recessesMedian dorsal

recessTwo lateral dorsal

recess

ANGLES Superior angle is continuous above with the cerebral

aqueduct of midbrain. Inferior angle is continuous below with the central canal of

the closed part of the medulla oblongata. Two lateral angles - lateral recess.

BOUNDARIES• On each side, the

fourth ventricle is bounded,

–Inferolaterally by inferior cerebellar peduncle, supplemented by gracile and cuneate tubercles, and

• Superolaterally, by superior cerebellar peduncle

ROOF Upper part:- convergence of two

superior cerebellar peduncles and

a thin sheet of white matter, the superior medullary velum.

Lower part:

- Inferior medullary velum.

- Median aperture of Magendie.

- T-shaped choroid plexus.

FLOOR (RHOMBOID FOSSA)

rhomboid in shape (diamond-shaped).

formed by posterior surfaces of the pons and the upper part of the medulla.

Three parts:A] Upper triangular part - The posterior surface of the pons.B] The lower triangular part - the upper part of the posterior surface of the medulla.C] The intermediate part at the junction of the medulla and pons.

FEATURES OF THE FLOOR OF FOURTH VENTRICLE Median sulcus.

Medial eminence.

Medial eminence is bounded laterally by sulcus limitans.

lateral to sulcus limitans. overlies the vestib-ular nuclei, hence it is termed vestibular area.

Superior fovea - upper end of sulcus limitans widens into a triangular depression.

Above the superior fovea the sulcus limitans flattens out and presents a bluish grey area called locus ceruleus.

The lowermost part of sulcus limitans presents a small depression called inferior fovea.

• On either side, the medial eminence, an oval swelling, facial colliculus.

• Sulcus divides the medial eminence, the hypoglossal triangle above and the vagal triangle below.

• The features of the lower part of the floor of fourth ventricle resemble with that of a pen-nib, hence it is called calamus scriptorius

The inferolateral margins -Marked by a narrow white ridge called taenia.

The two taenia

meet at the inferior angle of the ventricle to form a small fold called obex.

The term obex is

often used to denote the inferior angle of the fourth ventricle.

THANK YOU