In the temporal bone

Temporal bone

The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...

, between the posterior wall of the external acoustic meatus and the posterior root of the zygomatic process

Zygomatic process of temporal bone

The zygomatic process of the temporal bone is a long, arched process projecting from the lower part of the squamous portion of the temporal bone...

 is the area called the suprameatal triangle, mastoid fossa, foveola suprameatica, or Macewen

William Macewen

Sir William Macewen, CB, FRS, was a Scottish surgeon. He was a pioneer in modern brain surgery and contributed to the development of bone graft surgery, the surgical treatment of hernia and of pneumonectomy .-Career:Macewen was born near Port Bannatyne, Isle of Bute, Scotland in 1848 and studied...

's triangle, through which an instrument may be pushed into the mastoid antrum

Mastoid antrum

The mastoid antrum is a cavity in the petrous portion of the temporal bone, communicating posteriorly with the mastoid cells and anteriorly with the epitympanic recess of the middle ear via the aditus to mastoid antrum .-External links: - "Illustration of the continuity of the...

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In the adult, the antrum lies approximately 1.5 to 2 cm deep to the suprameatal triangle. This is an important landmark when performing a cortical mastoidectomy.
The supreameatal triangle lies deep to the cymba conchae.