Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact with the retromandibular part of the parotid gland.

Internally, the tympanic part is fused with the petrous portion, and appears in the retreating angle between it and the squama, where it lies below and lateral to the orifice of the auditory tube.

The central portion of the tympanic part is thin, as it gives rise to the bony inner two-thirds of the ear canal, and in 5 - 20% of skulls the lower surface is perforated by a hole, the foramen of Huschke[1] that opens onto the temporomandibular joint due to incomplete fusion of the anterior and posterior prominences during development.

In sagittal section it presents an oval or elliptical shape with the long axis directed downward and slightly backward.

bullae) is a hollow bony structure on the ventral, posterior portion of the skull that encloses parts of the middle and inner ear.