The skull vault, also called calvarium or skull cap is the protective case of the brain. It is formed of flat bones forming the roof and sides of the skull. It constitutes with base of the skull the neurocranium. The neonatal vault is composed of pairs of the following separate bones: parietal, most of the two frontal and the squamous part of temporal bones as well as the squamous part of the single occipital bone 8. These bones are connected by narrow straight areas of fibrous tissues widened at the meetings of more than two bones to form large gaps closed by tough membranes and known as fontanelles (Figure 1).

Ossification centers appear during the intrauterine life via intramembranous ossification within the outer layer of the condensed membrane surrounding the developing brain. These centers initiate the development of the individual bones forming the skull vault. The mesoderm in-between such individual bones forms fibrous tissues creating syndesmotic articulations called sutures 9.

The fontanelles are six in number including two singles: anterior "frontal" and posterior "occipital", and two pairs: anterolateral "sphenoidal" and posterolateral "mastoid". The parietal bone being situated centrally in the skull vault, it shares in the formation of all fontanelles 9. The more prominent fontanelle is the anterior rhomboidal one, situated between the two frontal and two parietal bones. The posterior fontanelle is triangular in shape lying at the junction of the two parietal bones with the occipital one. Other fontanelles are small 10. The fontanelles may reveal slight normal pulsation. The anterior fontanelle is the widest and the most clinical important one. It measures about 2.1 cm in size, and its median time to be closed is 13.8 months. On the other hand, the posterior fontanelle is about 0.5- 0.7 cm in size; and closes by the second month 11.

While bones of skull vault ossify through intramembranous ossification from bone centers appearing in the connective tissue membrane by the 8^th week of intrauterine life, bones forming the skull base are formed by endochondral ossification 8,12. During infancy, the bony plates of skull vault resolve to form two tables 'outer and inner' of compact bones with intervening cancellous diploë. Also, within the first postnatal months, the fontanelles become ossified and disappear; and bones come close together forming sutures 13. The sutures appear as irregular lines resembling the surgical sutures or stitches; hence they might take their names.

Although the development of the brain is a continuous process throughout the life, the first years are the most important for healthy brain. Its development begins few weeks after conception and thought to be completed at the early adulthood 14. The developing brain is the primary inductor or initiative factor in appearance of the bones of the skull vault. Therefore, cases of anencephaly, in which there is failure of development of the cranial part of neural tube, are associated with absence of the skull vault. Moreover, failure of brain growth could lead to microcephaly 8. This is also marked in case of hydrocephalus occurring due to marked distension of the brain caused by increased CSF. Such increased CSF occurring after fusion of the sutures could compress the delicate brain tissue causing difficulties in the brain functions and even its damage 15.

The process of brain myelination begins after birth and includes all lobes of the cerebrum by the end of the first year. Such process is correlated to attaining certain cognitive abilities 6.

The sites of sutures between the fetal bones give flexibility for the head to pass through the birth canal. These bones being separate entities override each other at birth to decrease the diameters of the delivered head 16. However, after birth the bones return away from each other to allow postnatal brain development. Later on, they become adherent together at more or less fixed "fibrous" joints called sutures. Mature closure of the sutures occurs by the age 12 years and completed at the third decade 12.

Variant sized skull vault of the neonates at birth should be investigated to determine its cause. Small sized vault might be due to brain cause including fetal alcohol syndrome and infections such as rubella, toxoplasmosis and herpes simplex. On the other hand, enlarged size might be caused by skeletal dysplasia or increased intracranial volume such as cases of hydrocephalus 17.

Margulies and Thibault concluded that the cranial sutures of the infant skull are weak; and have no the shock absorbing capabilities present in that of adults 18.

Despite the fontanelles are closed by strong membranes, they should be considered as potential weak points. The mothers and paramedical staffs should be oriented to such points. These fontanelles have been used in ultrasonography imaging of the neonatal cranial cavity and brain 19.

Palpation of the fontanelles at labor helps in diagnosis of the position of the head. Also, their inspection could assist in diagnosis of the state of growth of the surrounding bones; and to check the degree of dehydration and intracranial pressure. Cases of severe dehydration or malnutrition are commonly associated with depressed 'sunken' fontanelles; while increased intracranial tension causes their bulging 8. Abnormally large anterior fontanelle with an open posterior one is an early sign of the hypothyroidism. Also, these signs might denote other underlying causes such as increased intracranial pressure, achondroplasia, Down syndrome and rickets. On the other hand abnormal premature closure of the sutures might occur in craniosynostosis and abnormal brain development. Any abnormal size necessitates careful monitoring of the skull circumference to exclude pathologic causes 11.