Petrous part of temporal bone

The petrous part of the temporal bone is pyramid-shaped and is wedged in at the base of the skull between the sphenoid and occipital bones.

Directed medially, forward, and a little upward, it presents a base, an apex, three surfaces, and three angles, and houses in its interior, the components of the inner ear.

The petrous portion is among the most basal elements of the skull and forms part of the endocranium.

Petrous comes from the Latin word petrosus, meaning "stone-like, hard". It is one of the densest bones in the body.

BASE

The base is fused with the internal surfaces of the squamous and mastoid parts.

APEX

The apex, which is rough and uneven, is received into the angular interval between the posterior border of the great wing of the sphenoid bone and the basilar part of the occipital bone; it presents the anterior or internal opening of the carotid canal, and forms the postero-lateral boundary of the foramen lacerum.

SURFACES

• ANTERIOR SURFACE

The anterior surface forms the posterior part of the middle cranial fossa of the base of the skull, and is continuous with the inner surface of the squamous portion, to which it is united by the petrosquamous suture, remains of which are distinct even at a late period of life.

It is marked by depressions for the convolutions of the brain, and presents six notable points:

• near the center, the arcuate eminence (eminentia arcuata), which indicates the location of the superior semicircular canal.

• in front of and a little lateral to this eminence, a depression indicating the position of the tympanic cavity: Here, the layer of bone that separates the tympanic from the cranial cavity is extremely thin, and is known as the tegmen tympani