Ossification of lateral components in the human prenatal cranial base.

The purpose of the present study was to perform a radiographic description of the developing osseous structures in the prenatal human cranial base and to describe the sequence in which these structures ossify. The material consisted of 58 normal human fetuses (crown-rump length (CRL) 26-180 mm). The period investigated covered the time interval from the period before start of ossification at 8 weeks gestational age to occurrence of distinct ossification at 22 weeks gestational age. The osseous structures of 48 cranial bases were identified by radiography, supplemented by inspection of ten deviscerated cranial bases. The time of appearance of ossification of the individual bones was in agreement with former reports. The study showed a remarkable consistency in the sequence of ossification in the lateral part of the cranial base (parasagittal segment, PSS). The development was divided into eight stages. Bilateral agreement in ossification pattern was observed. The ossification pattern in the parasagittal segments of the cranial base was characterized by occurrence of osseous bone structures in the squama regions before occurrence in the cranial base region. It is suggested that a connection exists between the ossification pattern of the cranial base and the developmental pattern of the brain.