The frontal bone creates the smooth curvature of the forehead and protects the frontal lobe of the brain, especially the ethmoid bone's horizontal plate known as the cribriform plate which allows the olfactory nerve bundles to pass through its perforated surface and bring the ceiling of the nasal cavity its sense of smell. The frontal bone is involved in the three regions of the head, such are the forehead, the orbit and the nose.
Squamous - area of the forehead; it contains the frontal sinuses, superior border of the orbit, glabella, zygomatic processes
Orbital - forms the roof of the ethmoidal sinuses; it contains the anterior ethmoidal foramen (anterior ethmoidal nerve and vessels), posterior ethmoidal foramen (posterior ethmoidal nerve and vessels)
Nasal - stem of the nose
Coronal suture separates it from the parietal bone
Sphenofrontal suture separates it from the sphenoid bone
Zygomaticofrontal suture separates it from the zygomatic bone
Nasofrontal suture separates it from the nasal bone
Frontomaxillary suture separates it from the maxilla
|Articulations||Twelve bones: the sphenoid, the ethmoid, two parietals, two nasals, two maxillae, two lacrimals, two zygomatics|
This article will explain all the important anatmoical landmarks of the frontal bone.
- the squamous part
- the orbital part
- the nasal part
The largest area of the frontal bone is the squamous part which encompasses the area of the forehead. It comprises the frontal sinuses which are situated superior to the orbit on the medial side and are separated by a septum.
The superior border of the orbit (supraorbital margin) contains the supraorbital notch where the supraorbital vessels and nerve pass through. The arches above them are known as the superciliary arches (Latin “cilia” = eyelashes). The smooth and slightly elevated surface above the nasal root is referred to as glabella. The zygomatic processes arise caudolaterally from the squamous part and articulate with the zygomatic bone.
The orbital part forms the roof of the orbit and the ethmoidal sinuses. The ethmoid air cells lie within its ethmoidal notch. The trochlear spine serves as a site of insertion for the superior oblique muscle at the medial eye angle.
The orbital part comprises two openings: the anterior ethmoidal foramen ( for the anterior ethmoidal vessels and nerve) and posterior ethmoidal foramen (for the posterior ethmoidal vessels and nerve).
The bone is surrounded by no less than seven articulating bones. The adjacent bones and the corresponding sutures are:
The ossification of all three parts of the frontal bone is intramembranous. Sometimes a persistent metopic suture can be seen running down the midline of the frontal bone. This is a remnant of the original frontal suture that normally ossifies at two years of age. Another relic that can be present on the squamous part are the arachnoid foveae. These are thinner areas that have undergone bone resorption due to the pressure placed by the arachnoid granulations pushing on the dura mater.
In newborns, the frontal sinuses are merely small cavities without any openings. These start to develop from two years of age due to the upward migration of ethmoid air cells (secondary pneumatization) until early adolescence. The left and right frontal sinuses develop independently which is why one may have one dominant and one hypoplastic side.
The frontal bone is one of the skull bones enclosing the brain (neurocranium) and it consists of three parts:
- Squamous part - It is the largest one and encompasses the area of the forehead. It comprises the frontal sinuses. This part contains the supraorbital notch, the superciliary arches, the glabella, and zygomatic processes.
- Orbital part - It forms the roof of the orbit and the ethmoidal sinuses. In addition, this part comprises the anterior and posterior ethmoidal foramina.
- Nasal part - It is connected to the frontal processes of the maxilla and the nasal bones, forming the stem of the nose.