Right lateral view of mastoid process. For orientation, the left border of the image is superior, the top border is anterior. Soft tissue and periosteum have been removed to expose the mastoid process. The longissimus capitis muscle inserts into the posterior margin of the mastoid process. A notch on its medial side, the mastoid notch, is the site of attachment of the posterior digastric muscle. The Spine of Henle or suprameatal spine is a small projection of bone along the upper posterior margin of the opening of the external auditory canal. (Image courtesy of AL Rhoton, Jr.)