Which fissure separates the anterior from the posterior portion of the TMJ fossa?

• A. Petrotympanic fissure
• B. Stylomastoid foramen
• C. Foramen ovale
• D. Superior orbital fissure

Answer: (A)

The TMJ fossa is conceptually split into front and back parts by a small fissure that marks its boundary. The fissure that does this is the petrotympanic fissure. It lies between the tympanic part and the petrous part of the temporal bone, creating a natural division between the anterior articular area of the fossa and the posterior region near the middle ear. This fissure also transmits the chorda tympani nerve, which helps explain why it’s a notable landmark in the area around the temporomandibular joint.

The other openings are in different regions and serve other structures—stylomastoid foramen for the facial nerve exit, foramen ovale for the mandibular nerve, and the superior orbital fissure for nerves entering the orbit—so they don’t define the split within the TMJ fossa.