Osseous anatomy of the posterior skull base. Ventral view of the occipital, temporal, and sphenoid bones. The pterygoid portion of the sphenoid bone articulates with the body of the sphenoid or sphenoid sinus to form the pterygosphenoidal fissure. The pterygoid portion has a base and two plates, medial and lateral. The pterygoid base contains the vidian or pterygoid canal inferomedially and the foramen rotundum superolaterally. The notch for the palatosphenoidal artery is located at the same vertical level but just medial to the vidian canal. The pterygoid portion blocks access to the ventral petroclival fissure, foramen lacerum, and jugular foramen; access to these areas requires a transpterygoid approach. (Image courtesy of JC Fernandez-Miranda)