Growth of the cranial bones in human fetuses (2nd and 3rd trimesters).

The increase of the weight of some cranial bones was studied in 30 human fetuses (from 17 to 41 weeks of gestation, both sexes together) by multivariate allometry. The study was performed with a covariance matrix of the log-transformed bony weights and the Principal Components Analysis (PCA). The first principal component in PCA accounted for 92.12% of the total variance, and all characters were positively correlated with this component. PCA scaled the growth of the bones in the following sequence: a) with negative allometry: vomer, palatine, mandible and maxillae; b) with isometry (p less than 0.05): zygomatic bone; c) with positive allometry: sphenoid, ethmoid, frontal, occipital, temporal and parietal. During the 2nd and 3rd trimesters of gestation the skull exhibited two different growth rates, i.e., the bony group of the facial skeleton presented lower eigenvalues than the bony group of the calvaria, including the base of the skull. These bones of the calvaria certainly are affected by the high increase in volume of the fetal brain during the prenatal life. The knowledge of the cranial growth is a useful information for the anatomy, anthropology, orthodontics, and several medical specialties: radiology, obstetrics, pediatrics, orthopedics and reconstructive surgery.