The opisthion is the midpoint on the posterior margin of the foramen magnum. The occipital condyle is wider than the foramen magnum. C1 ring to enter the foramen magnum. The basion is located at the midpoint on the anterior margin of the foramen magnum. There are two midline skull landmarks at the foramen magnum. The spinal cord passes through the foramen magnum. The foramen magnum is a very important feature in bipedal mammals. The skull is large, with a narrow foramen magnum, and relatively small skull base. On the occipital bone the foramen magnum presents two midline cephalometric landmarks. The jerboa, a bipedal rodent, also has a foramen magnum. Other uncommon locations are the lateral ventricle, foramen magnum, and the orbit/optic nerve sheath. Other birdlike characters included the palatine, foramen magnum, cervical and caudal vertebrae, and many others. The foramen magnum is triangular in the North American beaver, and rounded in the European. The foramen magnum migrated under the skull and more anterior. The "foramen magnum" is rounded in the Eurasian beaver and triangular in the North American.