The mastoid process is a conical prominence projecting from the undersurface of the mastoid portion of the temporal bone. It is located just behind the external acoustic meatus, and lateral to the styloid process. Its size and form vary somewhat; it is larger in the male than in the female. This process serves for the attachment of the posterior belly of the digastric, sternocleidomastoid, splenius capitis, and longissimus capitis muscles. The word is derived from the Greek 'masto-', alluding to its resemblance to the breast. [ http://en.wikipedia.org/wiki/Mastoid_process ]