General
- It is a bowl-shaped bone
Comprising three parts:
- Squamous Part
- It is the largest area of the bone, encircling the forehead.
- Its external side is flat, but the internal side is concave.
- Two thickened regions, the supraorbital notches or supraorbital ridges, form the characteristic shape of the two brows and the anterior cover for the frontal sinuses.
- Deep into the supraorbital ridges are a pair of hollow spaces known as the frontal sinuses.
- These sinuses connect to the nasal cavity and are lined with mucous membranes.
- Though their exact function is unknown, the hollow spaces are believed to make the skull lighter and improve vocal tone by increasing the resonance of the skull.
- Orbital Part
- This part of the bone forms the roof of the eye orbit and the ethmoidal sinuse.
- The orbital part consists of two orbital plates separated by a gap known as the ethmoidal notch.
- The ethmoid air cells lie within this notch.
- There are two openings at the front and back of this part, the anterior ethmoidal foramen and posterior ethmoidal foramen.
- These foramina allow the passage of anterior and posterior ethmoidal vessels and nerves, respectively.
- The orbital part also features another important bony landmark, called the trochlear spine or fovea trochlearis which serves as an insertion site for the superior oblique muscle.
- Nasal Part
- This part of the bone is present between the brow ridges, hence the name.
- It ends in a serrated nasal notch that articulates inferiorly with the nasal bones and laterally with the frontal processes of the maxilla and lacrimal bones.
- The stem of the nose is formed due to these articulations.
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