Anterior surface of petrous part

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

• a shallow groove, sometimes double, leading lateralward and backward to an oblique opening, the hiatus for greater petrosal nerve, for the passage of the greater petrosal nerve and for the petrosal branch of the middle meningeal artery

• lateral to the hiatus, a smaller opening, occasionally seen, for the passage of the lesser superficial petrosal nerve

• near the apex of the bone, the termination of the carotid canal, the wall of which in this situation is deficient in front

• above this canal the shallow trigeminal impression for the reception of the trigeminal ganglion.