What is the Frontal Bone
Frontal bone is one of the eight cranial bones that form the cranium. In Latin ‘frons’ stands for ‘forehead’, which gives the bone its name as it forms the smooth curve of the forehead. Along with forehead, the bone also partially forms the bony part of the nose, and the upper ridge and roof of the eye orbit. This unpaired bone supports and protects the delicate nervous tissues of the brain, supports several muscles of the head, and gives a characteristic shape to the skull.
Where is the Frontal Bone Located
The frontal bone is located in front of the skull, more specifically, above the nasal bones and in front of the parietal bones. You can easily feel the bone by touching your forehead.
|How many are there in the human body||1|
|Articulates with||12 bones: sphenoid, ethmoid, parietal (2), nasal (2), maxillae (2),lacrimal (2), and zygomatic (2) bones|
- Protects the frontal lobe of the brain.
- Supports the structures of the head, such as the eye orbits and nasal passages.
- Aids facial expression through its muscle attachments.
- Plays a major role in a person’s appearance.
Frontal Bone Anatomy
It is a bowl-shaped bone, comprising three parts: the squamous part, the orbital part, and the nasal part.
1. Squamous Part
It is the largest area of the bone, encircling the forehead. Its external side is flat, but the internal side is concave. The part has two thickened regions called the supraorbital notches or supraorbital ridges. These ridges form characteristic shape of the two brows and the anterior cover for the frontal sinuses.
Deep to the supraorbital ridges, there is a pair of hollow space known as the frontal sinuses. These sinuses connect to the nasal cavity and are lined with mucous membranes. The frontal sinuses remain separated by a septum and are believed to reduce the weight of the skull by being hollow and increase the resonance of the skull to improve vocal tone.
Above each orbit in the supraorbital ridge, two small holes, known as the supraorbital foramina, are found. The supraorbital nerve and vessels exit through these foramina. The inferior end of each supraorbital ridge features the supraorbital margin. Here, the bone forms a sharp angle to form the superior and medial margins of the eye orbits. Inside the orbits, the bone continues posteriorly along the superior margin until it meets the sphenoid bone. It also continues inferiorly along the medial margin until it joins the ethmoid and lacrimal bones.
The arches above the supraorbital notches are known as the superciliary arches. Medial to the supraorbital ridges, a small, smooth, slightly elevated surface called glabella is present that ends inferiorly at the nasal bones.
It also contains a small zygomatic process that arises caudolaterally. The bone articulates with the zygomatic bone via this process.
2. Orbital Part
This part of the bone forms the roof of the eye orbit and the ethmoidal sinuses, lying between the eyes and nose. 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 that serves as an insertion site for the superior oblique muscle.
3. 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.
Borders and Articulations
As stated, the bone articulates with two unpaired (sphenoid, ethmoid) and five paired (parietal, nasal, maxilla, lacrimal, zygomatic) bones via sutures. Below is the list of the articulating bones, along with their respective sutures:
- Sphenoid bone, via sphenofrontal suture
- Ethmoid bone, via frontoethmoidal suture
- Parietal bones, via coronal suture
- Nasal bones, via frontonasal suture
- Maxilla, via frontomaxillary suture
- Lacrimal bones, via frontolacrimal suture
- Zygomatic bones, via zygomaticofrontal suture
The temporalis and orbicularis oculi are two major facial muscles originating from the frontal bone. Another one, called the frontalis muscle, which forms the frontal belly of the epicranius muscle, passes over the smooth squamous part of the bone.
Ossification and Development
Like other skull bones, frontal bone is also derived from neural crest cells. The bone evolves as two separate parts at birth, joined by a frontal suture. The whole frontal suture undergoes intramembranous ossification at two years of age, except its anteriormost part that ossifies around eight years of age, but may even persist throughout life. This remnant suture is termed as the metopic suture.