A, The jugular foramen is located between the temporal and occipital bones. One can-not see directly through the foramen from above, as shown, because it is directed forward under the temporal bone. The sigmoid groove descends along the mastoid and crosses the occipitomastoid suture where it turns forward on the upper surface of the jugular process of the occipital bone and enters the foramen by passing under the posterior part of the petrous temporal bone. B, The view directed from posterior and superior shows the shape of the foramen, which is not seen on the direct superior view. The foramen has a larger lateral sigmoid part through which the sigmoid sinus empties and a smaller anteromedial petrosal part through which the inferior petrosal sinus empties. The two parts are separated by the intrajugular processes of the occipital and temporal bones. The glossopharyngeal, vagus, and accessory nerves pass through the intrajugular portion of the foramen located between the sigmoid and petrosal parts. The foramen is asymmetric from side to side with the right side often being larger as shown. The cochlear aqueduct opens just above the anterior edge of the petrosal part. The vestibular aqueduct opens into the endolymphatic sac, which sits on the back of the temporal bone superolateral to the sigmoid part of the jugular foramen. C, Jugular foramen viewed from directly below. One cannot see directly through the foramen from below because the foramen is covered above by the part of the petrous temporal bone forming the jugular fossa, which houses the jugular bulb. The entrance into the carotid canal is located directly in front of the medial half of the jugular foramen. The stylomastoid foramen is located lateral and the anterior half of the occipital condyle medial to the jugular foramen. The posterior condylar foramen is transversed by an emissary vein, which joins the sigmoid sinus. The hypoglossal canal passes above the middle third of the occipital condyle and opens laterally into the interval between the jugular foramen and carotid canal. D, The view directed from anterior and backward reveals the shape of the jugular foramen. The roof over the foramen formed by the jugular fossa of the temporal bone is shaped to accommodate the jugular bulb. The posterior margin of the foramen is formed by the jugular process of the occipital bone, which connects the basal (clival) part of the occipital bone to the squamosal part. The petroclival fissure intersects the anteromedial margin of the petrosal part of the foramen. (Images courtesy of AL Rhoton, Jr.)