Fetal Skull

• Protect the brain 

• Ability to change shape – adapting to the 

process of labour

• Skin
• Connective tissue – containing blood vessels and hair follicles. May become oedematous during labour resulting in caput succedaneum 
• Aponeurosis – fibrous sheet 
• Connective tissue – loose layer enabling movement of the scalp 
• Periosteum – double sheet of connective tissue covering and nourishing the bone. It is attached to the edges of the bone

• Large dome shaped area, containing the cerebral hemispheres 
• Bones are relatively thin and pliable to allow them to overlap during labour 
• It is composed entirely of membrane in early fetal life 
• At birth the membranes still remain between the bones at the sutures and fontanelles

Points of ossification:

•  Parietal eminences 
• Occipital protuberance
• Frontal bossess

• Occipital bone (1) – lies at the back of the head and form the region of the occiput. Part of it forms the base of the skull. At the centre is the Occipital Protuberance. 
• Parietal Bones (2) – lie on either side of the fetal skull, the centre of ossification of each is the Parietal Eminence. 
• Frontal Bones (2) – form the forehead (Sinciput). At the centre of each is a Frontal Boss or Eminence. Fuse to become one by the age of 8 years 
• Temporal Bones (2) – small, flat and form a small part of the vault at the side

• Composed of bones which are firmly united to protect the vital centres in the medulla. 
• Perforated by a circular opening FORAMEN MAGNUM – through which the spinal cord passes

• Composed of 14 small bones which are firmly united and non compressible

Face - Extends from the superorbita ridges to the chin

Brow - (sinciput) lies between bregma & root of the  nose 

Mentum - the chin 

Occiput - lies over the occipital bone 

Subocciputal - lies below the occipital protuberance 

Vertex - diamond shaped area between anterior & posterior fontanelles & parietal eminences

• Soft fibrous tissues linking some bones of the skull 
• Enable moulding of the head during labour 
• Enables expansion of the brain during childhood 

Frontal suture - between 2 frontal bones 

Sagittal suture - between 2 parietal bones 

Coronal suture - between parietal & frontal 

Lambdoidal suture - between parietal & occipital 

Temporal suture - between inferior margin of  the parietal & temporal

• Fontanelle – membranous, non ossified area of the skull where three or more sutures meet. 

•  Anterior fontanelle (Bregma) - diamond shaped space between coronal & sagittal suture, ossifies at 18 months 

• Posterior fontanelle (lambda) - triangle shaped space between sagittal & lambdoidal suture

Biparietal diameter 9.5 cm.

• between parietal eminences The greatest transverse diameter 

Suboccipitobregmatic 9.5 cm. 

• measured from the junction of the head with the neck just below the occipital protuberance to the  centre of the anterior fontanelle. 
•  The presenting diameter of the well flexed head in labour. 

Suboccipitofrontal 10 cm 

• measured from the junction of the head with the neck just below the occipital protuberance to the centre of  the frontal suture. 
• The presenting diameter of the partially flexed head.

• Occurs with descent of the fetal 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