Skull Development
normal skull anatomy and development
Neurocranium
Divides into the…
- Cranial vault, which provides a roof for the brain.
- Skull base, which provides a floor for the brain.
Viscerocranium
- Comprises the facial bones.
skull development
- The cranial vault and viscerocranium develop via intramembranous ossification (again, which has no intermediate cartilaginous model).
- The skull base develops via endochondral ossification, which develops via a cartilaginous matrix.
The cranial vault comprises:
- Frontal bone, Parietal bone, upper portion of the Occipital bone, and Squamous portion of the Temporal bone – all of these develop via intramembranous ossification.
The key bones of the the skull base:
- The lower portion of the Occipital bone, the Petrous portion of the Temporal bone, and the Sphenoid bone – all of these bones develop via endochondral ossification.
- Key viscerocranial bones:
- The bones of the face derive from embryonic cells from the pharyngeal arches (from neural crest cells (other than the laryngeal cartilages, which derive from mesoderm)).
Skull Sutures
- At birth, the skull has openings (sutures) to accommodate brain growth, because the cranial vault ossifies early via intramembranous ossification. These sutures allow the fetal skull to ossify quickly prior to delivery [via intramembranous ossification] (so the brain doesn't get squashed) and yet still accommodate skull distortion during birth (called, molding) and permit rapid brain growth during the first two years of life when the brain quadruples in size to 75 percent of its adult volume!
- Metopic - forms between midline aspects of the left/right aspects of the frontal bone.
- Coronal - lies between the frontal and parietal bones.
- Sagittal - lies between the bilateral parietal bones.
- Lambdoid - lies between the parietal bones and occipital bone.
- There are three additional minor sutures: frontonasal, temporosquamosal, and frontosphenoidal.
The fontanelles
The large openings that exist in the newborn calvarium.
- The frontal bone covers the majority of the anterior frontal lobes.
- The parietal bones cover the remainder and the parietal lobes.
- The occipital bone covers the occiput.
Anterior fontanelle
- Forms at the junction of the sagittal, coronal, and metopic sutures at the anterior of the skull – it's palpable in midline, just behind the forehead; it closes at 1.5 to 2 years of age.
Posterior fontanelle
- Forms from the intersection of the sagittal and lambdoid sutures; it closes at 3 - 6 months of age.