<P> The position and size of this foramen are very variable; it is not always present; sometimes it is situated in the occipital bone, or in the suture between the temporal and the occipital . </P> <P> The mastoid portion is continued below into a conical or pyramidal projection, the mastoid process, the size and form of which vary somewhat; it is larger in the male than in the female . It is also filled with sinuses, or mastoid cells . The mastoid process is located just behind the ear canal, and lateral to the styloid process . </P> <P> The mastoid process serves for the attachment of the sternocleidomastoid, the posterior belly of the digastric muscle, splenius capitis, and longissimus capitis . </P> <P> On the medial side of the process is a deep groove, the mastoid notch, for the attachment of the digastric muscle; medial to this is a shallow furrow, the occipital groove, which lodges the occipital artery . </P>

Lateral cranial bone that forms the mastoid process