Sutures are cranial joints and are formed where two bones adjoin. A fontanel is formed when two or more sutures meet.
Types of Sutures
- The lambdoidal suture is shaped like the Greek letter 'lambda' and separates the occipital bone from the two parietal bones.
- The sagittal suture lies between the parietal bones
- The coronal suture separates the frontal bones from the parietal bones, passing from one temple to the other.
- The frontal suture runs between the two halves of the frontal bone.
In summary:
- Frontal suture - between the two frontal bones.
- Sagittal suture - between the two parietal bones.
- Coronal suture - between the parietal and frontal bones
- Lambdoid suture - between the parietal and occipital bones.
- Temporal suture - between the inferior margin of the parietal and temporal bones.
Types of Fontanel
a) The posterior fontanel or lambda: is a diamond shaped space situated at the junction of the lambdoidal and sagittal sutures and it can be recognised vaginally.
b) Anterior fontanel (bregma) - is located at the junction of coronal, sagittal and frontal sutures (3 by 3 cm;, ossifies at 18 months); it can be felt or recognised vaginally
The sutures and fontanels consist of membranous spaces that allow for a degree of overlapping of the skull bones (moulding) during labour and delivery.
Moulding
- Occurs with the descent of the foetal head into the pelvis to reduce the head circumference.
- Frontal bones slip under parietal bones.
- Parietal bones override each other.
- Parietal bones slip under the occipital bone.
(The anterior fontanel is larger than the posterior fontanel)