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The sphenoid bone [note 1] is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of the occipital bone. The sphenoid bone is one of the seven bones that articulate to form the orbit. Its shape somewhat resembles that of a butterfly, bat or wasp with its wings extended.
The ethmoid articulates with thirteen bones: two bones of the neurocranium—the frontal, and the sphenoid (at the sphenoidal body and at the sphenoidal conchae). eleven bones of the viscerocranium—, two nasal bones, two maxillae, two lacrimals, two palatines, two inferior nasal conchae, and the vomer.
The ethmoid bone (or a part of it) and also the sphenoid bone are sometimes included, but otherwise considered part of the neurocranium. Because the maxillary bones are fused, they are often collectively listed as only one bone. The mandible is generally considered separately from the cranium.
The superior surface of the body [Fig. 1] presents in front a prominent spine, the ethmoidal spine, for articulation with the cribriform plate of the ethmoid bone; behind this is a smooth surface slightly raised in the middle line, and grooved on either side for the olfactory lobes of the brain.
The frontal and sphenoid bones are towards the front middle of the skull and in front of the temporal bone. The ethmoid bone is the bone at the roof of the nose that separates the nasal cavity from the brain. It is a part of the dorsal cavity the cranial cavity and the spinal cord. The occipital bone is at the back of the skull.
In humans, the neurocranium is usually considered to include the following eight bones: 1 ethmoid bone; 1 frontal bone [5] 1 occipital bone; 2 parietal bones; 1 sphenoid bone; 2 temporal bones; The ossicles (three on each side) are usually not included as bones of the neurocranium. [6] There may variably also be extra sutural bones present.
Including the bones of the middle ear and the hyoid bone, the head contains 29 bones. Cranial bones (8) Occipital bone; Parietal bones (2) Frontal bone; Temporal bones (2) Sphenoid bone (sometimes counted as facial) Ethmoid bone (sometimes counted as facial) Facial bones (15) Nasal bones (2) Maxilla (upper jaw) (2) Lacrimal bone (2) Zygomatic ...
The spine is the place in the human body where the most irregular bones can be found. There are, in all, 33 irregular bones found here. The irregular bones are: the vertebrae, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid.