The petrotympanic fissure (squamotympanic fissure, Glaserian fissure) is a fissure in the temporal bone that runs from the temporomandibular joint to the tympanic cavity.
The mandibular fossa is bounded, in front, by the articular tubercle; behind, by the tympanic part of the bone, which separates it from the external acoustic meatus; it is divided into two parts by a narrow slit, the petrotympanic fissure.
It opens just above and in front of the ring of bone into which the tympanic membrane is inserted; in this situation it is a mere slit about 2 mm. in length. It lodges the anterior process and anterior ligament of the malleus, and gives passage to the anterior tympanic branch of the internal maxillary artery.
The contents of the fissure include communications of cranial nerves VII and IX to the infratemporal fossa. A branch of cranial nerve VII, the chorda tympani, runs through the fissure to join with the lingual nerve providing special sensory (taste) innervation to the tongue. The tympanic nerve branches off of cranial nerve IX to pass through the fissure as the lesser petrosal nerve, which passes through the foramen ovale and joins V3 of the trigeminal nerve, synapses in the otic ganglion, to provide parasympathetic innervation to the parotid gland.