Frontal Bone

Frontal bone: One of The Skull Bone

The skull is one of the most important structures of the human body. It is a complex arrangement of bones that houses and protects the brain, the most important organ of the body. The skull is not only responsible for protecting the brain but also serves as an attachment point for various muscles, ligaments, and tendons.

The skull is composed of 22 bones, which are joined together by sutures. These bones are divided into two main groups: the cranium and the face. The cranium, which is also known as the skullcap, forms the superior aspect of the skull and encloses the brain. The face is the front part of the skull and is responsible for housing the facial features.

The cranium is further divided into two parts: the roof and the base. The roof of the cranium is composed of the frontal, parietal, and occipital bones, while the base of the cranium is made up of the ethmoid, sphenoid, and temporal bones. The base of the cranium is further divided into two parts: the calvarium, which is the top part of the skull, and the cranial base, which forms the bottom part of the skull.

The frontal bone is a single, unpaired bone that is located in the front of the skull. It contributes to the formation of the cranium and is responsible for protecting the front part of the brain. The frontal bone is located superior to the nasal bone and anterior to the parietal bone. It forms the forehead region and is bowl-shaped, resembling a cockleshell in appearance.

In addition to protecting the brain, the frontal bone also serves as an attachment point for various muscles and ligaments. It is responsible for anchoring the muscles of the forehead, which are responsible for facial expressions such as frowning and raising the eyebrows. It also serves as an attachment point for the temporalis muscle, which is responsible for jaw movement during chewing.

Parts of Frontal Bone:

The frontal bone is a vital part of the skull that helps to protect the brain and supports various muscles and ligaments. It is a single unpaired bone that is located in the forehead region of the skull. The frontal bone contains several distinct parts, including:

  • The vertical part or squamous part:
    • This is the largest part of the frontal bone and forms the forehead region. It is a flat, plate-like structure that extends from the eyebrows to the top of the head.
  • The horizontal parts or orbital plates:
    • These are two thin, flattened bony plates that extend from the squamous part of the frontal bone to form the roof of the eye sockets. The orbital plates are responsible for protecting the eyes and also serve as attachment points for several muscles.
  • The nasal part:
    • This is a small, thin, rectangular-shaped part of the frontal bone that forms the upper part of the nasal cavity. The nasal part is located between the two orbital plates and helps to support the nose and protect the nasal cavity.

In addition to these parts, the frontal bone also contains several foramina, or small openings, that allow for the passage of blood vessels and nerves. The supraorbital foramen, for example, is a small opening located above the eye socket that allows for the passage of the supraorbital nerve and artery.

Anatomical Position of Frontal Bone:

The frontal bone is a key component of the skull and has a distinct anatomical position that helps to protect the brain and support various facial structures. Some of the key features of the anatomical position of the frontal bone include:

  • Orbital plates looking downwards:
    • The two thin, flattened bony plates that form the roof of the eye sockets, known as the orbital plates, are angled downwards. This helps to protect the eyes and also supports the muscles that control eye movement.
  • Nasal spine projecting downwards and forwards:
    • The nasal spine is a small, pointed projection that extends from the lower part of the nasal part of the frontal bone. It projects downwards and forwards, helping to support the nasal cavity and protect the delicate structures of the nose.
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Surfaces of Frontal Bone: 

The frontal bone is a flat, plate-like structure located at the front of the skull. It has several distinct surfaces that serve different functions, including:

  1. External or frontal surface:
    • This is the outermost surface of the frontal bone and forms the forehead region. It is a smooth, slightly curved surface that is covered by skin and muscle.
  2. Internal or cerebral surface:
    • This surface of the frontal bone faces inward and forms the roof of the frontal lobes of the brain. It is a relatively smooth surface that is marked by a few ridges and depressions that correspond to the underlying brain structures.
  3. Right lateral or temporal surfaces:
    • These are the two flat, plate-like surfaces that form the sides of the frontal bone. They are located on either side of the bone and are responsible for supporting various muscles and ligaments.
  4. Left lateral or temporal surfaces:
    • These surfaces are similar to the right lateral or temporal surfaces but are located on the opposite side of the bone.
  5. Right orbital surface:
    • This is the surface of the orbital plate that forms the roof of the right eye socket. It is a smooth, curved surface that is responsible for protecting the eye and supporting the muscles that control eye movement.
  6. Left orbital surface:
    • This surface is similar to the right orbital surface but is located on the opposite side of the frontal bone.

External Surface

Main Features of the External Surface of the Frontal Bone:

  1. Frontal or Metopic Suture:
  • Present in about 9% of cases
  • Located in the lower median plane
  • Indicates the development of the frontal bone in two distinct segments, which fuse into one
  1. Frontal Tuberosities or Eminences:
  • Rounded elevations on each side of the median plane
  • Situated approximately 3 cm above the supraorbital margin
  • More prominent in young female skulls
  • Serve as bony landmarks
  1. Superciliary Arches:
  • Arched eminences located above the supraorbital margin on each side
  • Separated from the frontal tuberosity by a shallow arched groove
  • Result from the frontal air sinus
  • Larger in male skulls compared to female skulls
  1. Glabella:
  • Smooth elevation situated in the median part between the superciliary arches
  1. Supraorbital Margin:
  • Forms the upper concave margin of the orbital opening on each side
  • Separates the vertical part from the horizontal part (orbital plate)
  • Sharp and prominent in its lateral 2/3 and rounded in its medial 1/3
  • Ends laterally in the zygomatic process, which articulates with the frontal process of the zygomatic bone

Sub-features of the Supraorbital Margin:

a. Supraorbital Foramen (or Canal):

  • Located at the junction of the lateral 2/3 and medial 1/3
  • Transmits supraorbital vessels and nerves

b. Foramen for the Frontal Diploic Vein:

  • May be present just above or near the supraorbital notch

c. Supratrochlear or Frontal Notch (or Foramen):

  • Occasionally found medial to the supraorbital notch
  • Transmits supratrochlear (frontal) vessels and nerves
  1. Nasal Part:
  • A portion of the bone that projects downward below the glabella and between the supraorbital margins

Subfeatures of the Nasal Part:

a. Nasal Notch:

  • Irregular notch that articulates on either side of the midline (from medial to lateral) with the nasal bone, frontal process of maxilla, and lacrimal bone

b. Nasal Spine:

  • Pointed projection downward in the median plane from the lower part of the nasal notch
  • Forms a small part of the septum of the nose
  • Articulates in front with the nasal crest of the articulated nasal bones, behind with the perpendicular plate of the ethmoid bone, and below with the septal cartilage

c. Nasal Groove or Nasal Surface:

  • Located posteriorly as a very narrow grooved area on either side of the nasal spine
  • Forms a small part of the roof of the corresponding nasal cavity

Internal Surface

The internal surface of the skull plays a crucial role in supporting and protecting the brain. It is a deeply concave region that provides a secure housing for the frontal lobe of the brain and its surrounding meninges. The surface is marked by several features that serve important functions.

  • Sagittal Sulcus: This is a vertical groove in the median plane that lodges the anterior part of the superior sagittal sinus. The margins of the sulcus provide attachment to the falx cerebri, a membrane that helps to support and divide the cerebral hemispheres.
  • Frontal Crest: The frontal crest is formed by the union of the margins of the sagittal sulcus below. It provides attachment to the anterior part of the falx cerebri.
  • Foramen Caecum: The frontal crest ends below in a notch, which can be converted into a foramen by articulation with the alae of the crista galli of the ethmoid bone. This foramen can transmit a vein or veins from the nasal mucosa to the superior sagittal sinus, but it is usually blind.
  • Granular Foveolae: These are small irregular pits on each side of the sulcus that lodge arachnoid granulations. Arachnoid granulations are small structures that help to regulate the pressure of cerebrospinal fluid within the brain.
  • Impressions for Cerebral Sulci and Gyri: These impressions are located on each side of the median plane and provide space for the brain to occupy, allowing it to function efficiently.
  • Furrows for Meningeal Vessels: These furrows are also present on the internal surface of the skull and help to facilitate the flow of blood and other vital fluids throughout the brain.
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Temporal Surface

The temporal surface is a prominent area of the frontal bone that plays a crucial role in supporting the temporal lobe of the brain. It is separated from the frontal surface by the superior temporal line and forms the anterior part of the temporal fossa, a shallow depression on the side of the skull. The temporal surface is marked by two distinct lines that serve important functions.

The Superior Temporal Line is a well-defined ridge that provides attachment to the temporal fascia, a layer of connective tissue that covers the temporalis muscle. The temporal fascia is an essential structure that helps to protect and support the temporal lobe of the brain.

The Inferior Temporal Line, together with the surface below, gives origin to the temporalis muscle, a key muscle responsible for jaw movement during chewing and speaking. This muscle is attached to the coronoid process of the mandible and plays an important role in mandibular elevation.

Orbital Surface:

The Orbital Surface of the frontal bone is a crucial area that forms the inferior surface of the orbital plate. It is a smooth and concave region that comprises a significant portion of the roof of the orbital cavity, which houses the eyeball and its surrounding structures.

The orbital surface of the frontal bone is marked by several critical structures, including the supraorbital margin, which is a bony ridge that forms the superior rim of the orbit. This margin provides attachment to the supraorbital soft tissue structures, including the supraorbital nerve, artery, and vein. The infraorbital margin is another important feature that forms the inferior rim of the orbit and provides attachment to the soft tissue structures that pass through the infraorbital foramen.

Moreover, the orbital surface of the frontal bone contains several depressions and grooves that provide space for important structures such as the lacrimal gland, the ethmoidal air cells, and the trochlear fossa. The lacrimal gland produces tears, which help to keep the surface of the eye moist and clean. The ethmoidal air cells are small cavities within the ethmoid bone that are responsible for air exchange and are lined with mucus-producing cells that help to filter and humidify the air we breathe. The trochlear fossa is a groove located on the medial side of the orbital surface that provides space for the trochlear nerve, which is responsible for the movement of the superior oblique muscle.

Orbital parts

The orbital plates are two thin triangular plates that form a significant part of the roof of the orbits on either side of the median plane. These plates are marked by several distinctive features that serve important functions in supporting and protecting the structures of the eye.

  • Lacrimal Fossa: This is a shallow depression located in the anterolateral part of the orbital plate. It lodges the lacrimal gland, which produces tears that help to keep the surface of the eye moist and clean.
  • Trochlear Fossa or Spine: This structure lies below and behind the medial end of the supra-orbital margin and gives attachment to the fibrocartilaginous pulley of the superior oblique muscle. The superior oblique muscle is responsible for rotating the eyeball downward and outward.

In addition to the two plates, the orbital part also presents several other important features, including:

  • Ethmoidal Notch: This is a wide U-shaped gap that separates the medial margins of the two plates. The medial margins of the orbital plates present broken air cells that, when articulated with the cribriform plate of the ethmoid bone, form the ethmoidal air sinuses.
  • Anterior and Posterior Ethmoidal Canals: These are two transverse grooves that cross each margin of the ethmoidal notch, with similar grooves on the upper surface of the labyrinth of the ethmoid. These canals transmit the anterior and posterior ethmoidal vessels and nerves, respectively.
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Moreover, the posterior border of each orbital plate is thin and serrated and articulates with the anterior border of the lesser wing of the sphenoid bone. This articulation provides support and stability to the orbital plates and helps to protect the structures of the eye.

Additional Information:

Parietal border (Posterior border) of the vertical part:

The parietal border, also known as the posterior border, is a feature of the vertical part of the frontal bone. It is a thin and serrated border that runs along the back of the bone, forming the junction between the vertical part and the horizontal part of the bone. The parietal border articulates with the parietal bone to form the sagittal suture, which is a fibrous joint that runs along the midline of the skull. The serrations on the parietal border help to interlock with the serrations on the parietal bone, providing stability and support to the skull. The parietal border is an important structure that helps to protect the brain and maintain the structural integrity of the skull.

Bregma

Bregma is an anatomical landmark located on the skull that is formed by the intersection of the coronal and sagittal sutures. It is located at the top of the head, near the midpoint between the two ears. Bregma is commonly used as a reference point for mapping various regions of the brain and for determining the position of electrodes in electroencephalography (EEG) studies. In infants, bregma is a soft spot where the skull bones have not yet fused, but it typically closes by around 18 months of age. Bregma is an important landmark for medical professionals and researchers studying the brain and its functions.

Nasion


Nasion is a craniofacial landmark located on the skull, specifically on the midline between the two orbits and at the junction of the nasal and frontal bones. It marks the intersection of the frontonasal suture and the midline of the skull, and it is an important reference point for craniofacial anthropometry and surgery. The distance between the nasion and other landmarks, such as the sella turcica or the basion, is measured to assess the size and shape of the skull and to aid in the diagnosis of various conditions. Nasion is also used in forensic anthropology to identify individuals from their skeletal remains. In addition, nasion plays a critical role in the development and growth of the face, particularly the nasal region.

Frontal Air Sinuses

Frontal air sinuses, also known as frontal sinuses, are air-filled cavities located within the frontal bone of the skull, just above the eyebrows and behind the forehead. These sinuses are paired, meaning there is one on each side of the skull, and they are lined with a mucous membrane that produces mucus to help moisten and clean the nasal cavity.

The size and shape of the frontal sinuses can vary from person to person, and they can even be absent in some individuals. In some cases, the sinuses can become inflamed or infected, leading to conditions such as sinusitis.

Despite their small size, the frontal sinuses play an important role in the overall health and function of the respiratory system. They help to lighten the skull and provide insulation to the eyes and brain. In addition, they may play a role in vocal resonance and temperature regulation. Understanding the anatomy and function of the frontal sinuses is important for medical professionals in diagnosing and treating conditions that affect the respiratory system.

Summary

The frontal bone is one of the bones of the skull, and it plays a crucial role in protecting and supporting the nervous tissue of the brain. The cranium, which encloses and protects the brain, is formed by the frontal bone. The frontal bone consists of three parts and six surfaces, including the orbital surface, the nasal surface, and the internal surface. The orbital surface forms a major part of the roof of the orbital cavity and contains several important structures, such as the supraorbital margin and the infraorbital margin. The nasal surface helps to form the bridge of the nose and contains the frontal sinuses. The internal surface of the frontal bone is deeply concave and lodges the frontal lobe of the brain with its meninges. The frontal bone also contributes to giving shape to the skull, and its features can be used to identify different regions of the skull. Overall, understanding the structure and function of the frontal bone is essential for medical professionals and researchers studying the brain and its surrounding structures.

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