Mastoid process

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Description:

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 cavities communicate with the middle ear via the mastoid antrum. They arise as diverticula of the mucous membrane that lines the mastoid antrum. They are not present at birth and form during early postnatal life. Attached to its external surface are the posterior belly of the occipitofrontalis, posterior auricular, longissimus capitis, splenius capitis, and sternocleidomastoid muscles.