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Other Terms: Mastoid portion of temporal bone, Processus mastoideus, Processus mastoïde
This is the rounded projection of bone behind the ear. It is variable in size, being very small in adolescence and increasing in prominence by adulthood. It is typically larger in males than in females. The bone is pneumatized with the mastoid air cells. These hollow air cells form connections with the middle ear via the mastoid antrum. They arise as diverticula of the membrane that lines the mastoid antrum. They are not present at birth and form during early postnatal life. The external surface of the bone provides attachment to the posterior belly of the occipitofrontalis, posterior auricular, longissimus capitis, splenius capitis, and sternocleidomastoid muscles.
Mastoid comes from the Greek mastos meaning breast. Galen used this name to describe a process of the temporal bone because he thought it resembled a breast in appearance. Process is a term used in anatomy to describe a projection on a bone. It comes from the Latin pro- meaning forward and cessus for gone. It is an old term that can be traced back to the writings of the early anatomist Celsus.