Foramen magnum in the context of "Bipedal"

The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal cord is hollow and contains a structure called the central canal, which contains cerebrospinal fluid. The spinal cord is also covered by the meninges and enclosed by the neural arches. Together, the brain and spinal cord make up the central nervous system.

In humans, the spinal cord is a continuation of the brainstem and anatomically begins at the occipital bone, passing out of the foramen magnum and then enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it tapers to become the cauda equina. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) long in adult men and around 43 cm (17 in) long in adult women. The diameter of the spinal cord ranges from 13 mm (1⁄2 in) in the cervical and lumbar regions to 6.4 mm (1⁄4 in) in the thoracic area.

The occipital bone (/ˌɒkˈsɪpɪtəl/) is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lobes of the cerebrum. At the base of the skull in the occipital bone, there is a large oval opening called the foramen magnum, which allows the passage of the spinal cord.

Like the other cranial bones, it is classed as a flat bone. Due to its many attachments and features, the occipital bone is described in terms of separate parts. From its front to the back is the basilar part, also called the basioccipital, at the sides of the foramen magnum are the lateral parts, also called the exoccipitals, and the back is named as the squamous part. The basilar part is a thick, somewhat quadrilateral piece in front of the foramen magnum and directed towards the pharynx. The squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone.

The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline.

In the young skull, this area is rough and uneven, and is joined to the body of the sphenoid by a plate of cartilage.

The lateral parts of the occipital bone (also called the exoccipitals) are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas.

The squamous part of occipital bone is situated above and behind the foramen magnum, and is curved from above downward and from side to side.

The tectorial membrane of atlanto-axial joint (occipitoaxial ligaments) is a tough membrane/broad, strong band representing the superior-ward prolongation of the posterior longitudinal ligament (the two being continuous).

It attaches inferiorly onto (the posterior aspect of) the body of axis. It broadens superiorly. Superiorly, the membrane extends deep to the median atlanto-axial joint and its associated ligaments, then through the foramen magnum into the cranial cavity where it ends by attaching onto the basilar part of occipital bone superior to the foramen magnum.

The clivus (/ˈklaɪvəs/, Latin for "slope") or Blumenbach clivus is a part of the occipital bone at the base of the skull, extending anteriorly from the foramen magnum. It is related to the pons and the abducens nerve (CN VI).

The term is also used for the clivus ocularis, an unrelated feature of the retina.