A, The soft palate, which has been preserved, is located at the level of the foramen magnum. The infratemporal fossa, located below the greater sphenoid wing and middle cranial fossa, contains the pterygoid muscles, maxillary artery, mandibular nerve branches, and the pterygoid venous plexus and opens posteriorly into the area around the carotid sheath, as shown on the left side. B, Enlarged view. The soft palate has been divided in the midline and the leaves reflected laterally. The atlanto-occipital joints and the foramen magnum are located at approximately the level of the hard palate. The anterior arch of C1 and the dens are located behind the oropharynx, and the clivus is located behind the nasopharynx and sphenoid sinus. The prominence over the longus capitis and the anterior arch of C1 are seen through the pharyngeal mucosa. C, The mucosa lining the posterior pharyngeal wall has been reflected to the right, exposing the longus capitis that attaches to the clivus and the part of the longus colli that attaches to the anterior arch of C1. The eustachian tube has been divided. The rectus capitis anterior extends from the transverse process of C1, posterolateral to the longus capitis, to attach to the occipital bone in front of the occipital condyle. D, The clivus and anterior arch of C1 have been removed. The dura has been opened to expose the vertebral and basilar artery. The dens has been preserved. The structures in the right infratemporal fossa and part of the right carotid artery and mandible have been removed to expose the right vertebral artery ascending between the C2 and C1 transverse processes. E, Enlarged view of the step between C and D. The anterior arch of C1 has been removed to expose the odontoid process and the lower part of the clivus. The left longus coli and longus capitis have been reflected out of the exposure. The atlanto-occipital joint is exposed at the level of the odontoid apex. The transverse part of the cruciform ligament, also called the transverse ligament, extends across the back of the dens and attaches to a tubercle on the medial side of each lateral mass of the axis. The tectorial membrane, a cephalic extension of the posterior longitudinal ligament, lines the posterior clival surface. The alar ligaments attach to the lateral edges of the foramen magnum. F, Enlarged view of the exposure shown in D. G, Exposure after opening of the clivus. Both vertebral and anteroinferior cerebellar arteries (AICAs) and the anterior spinal artery are exposed. (Images courtesy of AL Rhoton, Jr.)