The measurement of the skull is transverse, anteroposterior (longitudinal transverse) called diameters of the fetal skull.

a) Transverse diameters - Biparietal diameter: 9.5 cm between the parietal eminences - Bitemporal diameter: 8.2 cm between the points of the coronal suture at the temples (the part between the eye and the ear).

b) Antero-posterior or longitudinal diameters (see figure 2.3. below)

Sub occipito-bregmatic: 9.5 cm from below the occipital protuberance(that projects above the surface) to the centre of the anterior fontanels or bregma
Sub occipito-frontal: 10 cm from below occipital protuberance to the centre of the frontal suture.
Occipito-frontal: 11.5 cm from the occipital protuberance to the glabella (flat area forehead between the eye brows).
Mento-vertical: 13.5 cm from the point of the chin to the highest point on the vertex slightly nearer to the posterior than to the anterior fontanels.
Sub-mento-vertical: 11.5 cm from the point where the chin joins the neck to the highest point on the vertex.
Sub-mento-bregmatic: 9.5 cm from the point where the chin joins the neck to the centre of the bregma.

Fig 2.3. Diameters of the fetal skull.

The mento-vertical diameter of the skull is the longest while the bi-temporal is the shortest not suitable for childbirth.