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The frontal bone develops from membranous tissue. Only the nasal spine develops from cartilaginous tissue
Ossification:
- Occipital bone:
Lower part of the occipital bone including the supra-occiput develops from cartilaginous tissue.
The inter-parietal occiput develops from membranous tissue.
- Sphenoid bone:
The body, the lesser wings and the lower part of the greater wings develop from cartilage:
Both pterygoid processes and the upper part of the greater wings develop from membranous tissue.
- The ethmoid bone and the vomer develop from cartilage.
- Temporal bone:
The petrous portion develops from cartilage
The squamous portion and the tympanic portion develop from membran.
The petrous portion is the part of the skull which ossifies first. In the 22nd foetal week the ossification of the auditory system is already completed. At birth the squamous portion and the tympanic portion are already partly connected, forming the tympano-squamous fissure, which can be a possible location for intraosseous dysfunctions.
The squamous portion, the petrous portion and the styloid process melt together during the first year.
The mastoid process doesn’t develop until after the second year and can not be palpated on a newborn.
- The frontal bone develops from membranous tissue. Only the nasal spine develops from cartilaginous tissue.
In 85 to 90% of the cases, the metopic suture ossifies by the 7th year.
- The parietal bone ossifies from membrane. There is one ossification centre located in each parietal eminence.
- The maxilla and pre-maxilla are formed from membrane between the 7th and 8th foetal week.
The other bones also develop from membranous tissue.