( 3) The posterior cranial fossa It is the largest and deepest of the three cranial fossa The lowest part of the fossa presents the foramen magnum 枕骨大孔, There are hypoglossal canal 舌下神经管内口 above the anterolateral margin of the foramen magnum 经管 downUp down It is the largest and deepest of the three cranial fossa. The lowest part of the fossa presents the foramen magnum 枕骨大孔， There are hypoglossal canal 舌下神经管内口above the anterolateral margin of the foramen magnum. (3) The posterior cranial fossa