The rhomboid fossa is divided into symmetrical halves by a median sulcus which reaches from the upper to the lower angles of the fossa and is deeper below than above. On either side of this sulcus is an elevation, the medial eminence, bounded laterally by a sulcus, the sulcus limitans.

The median sulcus divides the floor into symmetrical halves. Each half is again divided into a medial eminence and a lateral area by the sulcus limitans.

Floor of the fourth ventricle: fc: facial colliculus; ht: hypoglossal triangle; if: inferior fovea; me: medial eminence; ms: median sulcus; o: obex; sf: superior fovea; sl: sulcus limitans; sm: medullary striae of fourth ventricle; vt: vagal triangle.

Ap: area postrema; icp: inferior cerebellar peduncle; lr: lateral recess; ms: median sulcus; scp: superior cerebellar peduncle; sf: superior fovea; sm: Medullary striae of fourth ventricle.