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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 squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone. Due to its embryonic derivation from paraxial mesoderm (as opposed to neural crest, from which many other craniofacial bones are derived), it has been posited that "the occipital bone as a whole could be considered as a giant ...
The singular basioccipital is the rear lower part of the braincase, below the foramen magnum. It is homologous to the basilar part of the occipital bone . In the ancestral tetrapod, the basioccipital makes up most of a large central knob-like surface, the occipital condyle, which articulates with the vertebrae as a ball-and-socket joint .
Several of these bones merge, and in the adult primates (including humans), the endocranium is composed of only five bony elements (from front to back): [4] The ethmoid bone, lying behind the nose. The sphenoid bone, underlying the forward portion of the brain; Paired petrous part of the temporal bones, containing the inner ear structures
A combination of a number of smaller bones (such as the basioccipital and exoccipitals) participate in the formation of this structure. In most dinosaurs, the occipital condyle is situated at the rear part of the skull, below the foramen magnum, and points toward the posterior of the animal.
The back part of the skull roof is incompletely known from the hind part of the lacrimal bone (in front of the eye opening), the postfrontal (above and behind the eye opening), the parietal (at the rear of the skull roof), and parts of a supratemporal that formed the rear corners of the skull roof.
This begins on the cranial surface of the bone immediately above the foramen magnum, and is directed lateralward and forward above the condyle. It may be partially or completely divided into two by a spicule of bone; it gives exit to the hypoglossal or twelfth cerebral nerve, and entrance to a meningeal branch of the ascending pharyngeal artery.
As is typical for reptiles, the lower rear portion of the braincase is formed by a bone known as the basioccipital, although this bone is unusually long and low in Vancleavea. The rear portion of the bone has a single large knob, known as an occipital condyle, which attaches the skull to the neck. A pair of bones outwards-angled known as ...