Bones of Skull

Introduction

The skull is the bony framework of the head that protects the brain and supports the structures of the face. It forms the skeleton of the head and provides attachment for muscles involved in facial expression, mastication, and head movements. The adult human skull consists of 22 bones, excluding the auditory ossicles.

Classification of Skull Bones

The skull is divided into two main parts:

1. Cranial Bones (Neurocranium) – 8 Bones

These bones form the cranial cavity and protect the brain.

2. Facial Bones (Viscerocranium) – 14 Bones

These bones form the face and provide attachment for facial muscles.

Cranial Bones

1. Frontal Bone

Location

Forms the forehead, roof of the orbit, and anterior cranial fossa.

Features

• Frontal squama
• Supraorbital margin
• Supraorbital foramen/notch
• Frontal sinus

Functions

• Protects frontal lobes of the brain
• Forms forehead
• Contributes to orbital cavity

2. Parietal Bones (Pair)

Location

Form the sides and roof of the cranium.

Features

• Parietal eminence
• Superior and inferior temporal lines

Functions

• Protect the brain
• Provide attachment for temporal muscles

3. Temporal Bones (Pair)

Location

Situated on either side of the skull.

Features

• External acoustic meatus
• Mastoid process
• Styloid process
• Zygomatic process
• Mandibular fossa

Functions

• House organs of hearing and balance
• Form temporomandibular joint (TMJ)
• Provide muscle attachment

4. Occipital Bone

Location

Forms the back and base of the skull.

Features

• Foramen magnum
• Occipital condyles
• External occipital protuberance

Functions

• Allows passage of spinal cord
• Articulates with atlas vertebra
• Protects cerebellum and brainstem

5. Sphenoid Bone

Location

Located at the base of the skull.

Features

• Butterfly-shaped bone
• Sella turcica
• Greater and lesser wings
• Pterygoid processes

Functions

• Supports pituitary gland
• Forms part of orbit and cranial floor
• Acts as a keystone of the skull

6. Ethmoid Bone

Location

Between the two orbits.

Features

• Cribriform plate
• Crista galli
• Perpendicular plate
• Ethmoidal air cells

Functions

• Forms roof of nasal cavity
• Supports olfactory nerves
• Contributes to nasal septum

Facial Bones

1. Maxillae (Pair)

Features

• Largest facial bones
• Contain maxillary sinuses
• Alveolar processes hold upper teeth

Functions

• Form upper jaw
• Form hard palate
• Contribute to orbit and nasal cavity

2. Mandible

Features

• Strongest facial bone
• Body and ramus
• Mandibular condyle
• Coronoid process

Functions

• Forms lower jaw
• Holds lower teeth
• Only movable bone of the skull

3. Zygomatic Bones (Pair)

Features

• Cheek bones
• Form zygomatic arch

Functions

• Form prominence of cheeks
• Contribute to orbital cavity

4. Nasal Bones (Pair)

Functions

• Form bridge of the nose
• Support nasal cartilages

5. Lacrimal Bones (Pair)

Features

• Smallest facial bones
• Contain lacrimal groove

Functions

• Accommodate lacrimal sac
• Assist tear drainage

6. Palatine Bones (Pair)

Functions

• Form posterior part of hard palate
• Contribute to nasal cavity and orbit

7. Inferior Nasal Conchae (Pair)

Functions

• Increase surface area of nasal cavity
• Warm, humidify, and filter inspired air

8. Vomer

Functions

• Forms lower part of nasal septum
• Divides nasal cavity into right and left halves

Sutures of the Skull

Sutures are immovable fibrous joints joining skull bones.

Major Sutures

1. Coronal Suture
   • Between frontal and parietal bones
2. Sagittal Suture
   • Between two parietal bones
3. Lambdoid Suture
   • Between parietal and occipital bones
4. Squamous Suture
   • Between temporal and parietal bones

Functions of the Skull

1. Protection

• Protects the brain and sensory organs.

2. Support

• Supports facial structures.

3. Muscle Attachment

• Provides attachment for muscles of mastication, facial expression, and neck.

4. Formation of Cavities

• Forms cranial, orbital, nasal, and oral cavities.

5. Passage for Nerves and Blood Vessels

• Numerous foramina allow passage of cranial nerves and vessels.

6. Hearing and Balance

• Temporal bones house organs of hearing and equilibrium.

7. Speech and Mastication

• Supports structures involved in chewing and speech.

Applied Anatomy

Skull Fractures

• May result from trauma.
• Can damage brain tissue and cranial nerves.

Fontanelles

• Soft membranous gaps between skull bones in infants.
• Allow brain growth and facilitate childbirth.

Deviated Nasal Septum

• Results from displacement of the vomer or ethmoid bone.

Temporomandibular Joint Disorders

• Affect movement of the mandible and chewing.

Conclusion

The skull is a complex bony structure consisting of 22 bones divided into 8 cranial bones and 14 facial bones. It protects the brain, supports facial structures, houses sensory organs, and provides attachment for muscles. Knowledge of skull bones is essential for understanding anatomy, physiology, neurology, dentistry, and clinical medicine.

Introduction

The skull is composed of several bones joined together by immovable fibrous joints known as sutures. In newborn infants, the bones of the skull are separated by membranous spaces called fontanelles, which facilitate childbirth and allow brain growth. Knowledge of sutures and fontanelles is important in anatomy, pediatrics, neurology, and forensic medicine.

Sutures of the Skull

Definition

Sutures are immovable fibrous joints (synarthroses) that unite the bones of the skull.

Functions of Sutures

• Hold skull bones together.
• Permit slight flexibility during birth.
• Allow growth of the skull during childhood.
• Protect the brain from mechanical injury.
• 

Major Sutures of the Skull

1. Coronal Suture

• Located between the frontal bone and two parietal bones.
• Extends from one side of the skull to the other.

Function: Joins the frontal bone with the parietal bones.

2. Sagittal Suture

• Located between the two parietal bones.
• Runs along the midline of the skull.

Function: Unites the right and left parietal bones.

3. Lambdoid Suture

• Located between the occipital bone and parietal bones.
• Appears lambda-shaped.

Function: Joins the occipital bone to the parietal bones.

4. Squamous Suture

• Found between the temporal bone and parietal bone.

Function: Connects the temporal bone with the parietal bone.

5. Metopic (Frontal) Suture

• Present between the two halves of the frontal bone in infants.
• Normally disappears by 6–8 years of age.

Clinical Significance: Persistence in adults is called a persistent metopic suture.

Fontanelles of the Skull

Definition

Fontanelles are soft membranous gaps between the skull bones of infants where sutures meet.

Functions

• Facilitate molding of the fetal head during birth.
• Permit rapid brain growth after birth.
• Allow assessment of infant health.

Types of Fontanelles

There are six fontanelles in the newborn skull.

1. Anterior Fontanelle (Bregma)

Location

At the junction of:

• Coronal suture
• Sagittal suture
• Frontal bones
• Parietal bones

Shape

Diamond-shaped.

Closure

Closes at 18–24 months.

Importance

• Largest fontanelle.
• Used to assess hydration and intracranial pressure.

2. Posterior Fontanelle (Lambda)

Location

At the junction of:

• Sagittal suture
• Lambdoid suture

Shape

Triangular.

Closure

Closes by 2–3 months after birth.

3. Anterolateral Fontanelles (Sphenoidal Fontanelles)

Number

Two (one on each side).

Location

At the junction of:

• Frontal
• Parietal
• Temporal
• Sphenoid bones

Closure

Around 6 months of age.

4. Posterolateral Fontanelles (Mastoid Fontanelles)

Number

Two (one on each side).

Location

At the junction of:

• Parietal
• Temporal
• Occipital bones

Closure

Between 6–18 months.

Clinical Importance of Fontanelles

1. Sunken Fontanelle

Indicates:

• Dehydration
• Severe malnutrition

2. Bulging Fontanelle

Indicates:

• Increased intracranial pressure
• Meningitis
• Hydrocephalus

3. Delayed Closure

Seen in:

• Rickets
• Hypothyroidism
• Hydrocephalus
• Down syndrome

4. Premature Closure (Craniosynostosis)

• Early fusion of skull sutures.
• Restricts brain growth.
• Produces abnormal skull shape.

Applied Anatomy of Skull Sutures

Craniosynostosis

Premature closure of one or more sutures causing skull deformities.

Cephalhematoma

Collection of blood beneath the periosteum of skull bones in newborns.

Skull Fractures

Fractures may follow suture lines and affect underlying brain structures.

Hydrocephalus

Excess cerebrospinal fluid causes enlargement of skull and delayed closure of fontanelles.

Forensic Importance

Suture closure helps estimate age in forensic investigations.

Conclusion

Sutures are fibrous joints that unite skull bones, while fontanelles are membranous gaps present in infants. They play essential roles in childbirth, skull growth, and brain protection. Their examination provides valuable information regarding neurological, developmental, and systemic disorders.