The inferior triangle of the rhomboid fossa is the part of the fossa below the striae medullares. It is formed by the medulla oblongata and a small portion of the pons. Inferior to the striae medullares, the fossa presents with two bilateral triangles (trigones):

Hypoglossal trigone or triangle - an elevated and triangular-shaped narrowing of the medial eminence; it houses the hypoglossal nuclei;
Vagal trigone or triangle - located laterally and downward from the previous triangle; it contains vagal nuclei.

Laterally to both mentioned triangles is the inferior fovea.

Each inferolateral margin of the rhomboid fossa contains narrow small white elevations or ridges called taenia, also known as taeniae of the fourth ventricle. The taenia extends from the striae medullares to the obex where the taenia from the left and right sides merge.

Below the vagal trigone, just before the obex, in the inferior part of the rhomboid fossa there is a small protuberance known as the area postrema. It is thought to be the vomiting control center, which induces vomiting in response to potential toxins. The area postrema is separated from the vagal trigone by a thin ridge named the funiculus separans.

The lowest part of the rhomboid fossa or its caudal ending is also known as the calamus scriptorius.

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Rhomboid fossa: inferior triangle