Ossification and midline shape changes of the human fetal cranial base.
An appreciation of ontogenetic changes to the cranial base is important for understanding the evolution of modern human skull form. Using geometric morphometric techniques, this study explores midline shape variations of the basicranium and midface during human prenatal ontogeny. In particular, the analysis sets out to explore shape variations associated with endochondral ossification and to reassess shape variations previously observed on the basis of angular measures.Fifty-four formalin-preserved human fetuses were imaged using high-resolution MRI. Coordinates for 10 landmarks defining the midline basicranium and midface were acquired and areas of ossification in the midline basioccipital, basisphenoid, and presphenoid cartilages were measured as percentages of overall cranial base area. The results show shape variations with increasing fetal size that are consistent with cranial base retroflexion, anterior facial projection and dorsal facial rotation. These growth variations are centered on the midsphenoid area and are associated with disproportionate variations of sphenoid height and length. Small but significant correlations were observed between ossification of the presphenoid cartilage and components of shape that described, among other variations, sphenoid shortening. While ossification cannot be directly linked with the shape variations observed, it seems likely that bone formation plays a role in modulating the influence of other factors on the fetal cranial base.
Jeffery
Nathan
N
Department of Human Anatomy and Cell Biology, University of Liverpool, Liverpool L69 3GE, United Kingdom. njeffery@liverpool.ac.uk
Spoor
Fred
F
D005075:Biological Evolution; D001846:Bone Development; D005260:Female; D005333:Fetus; D005865:Gestational Age; D006801:Humans; D008279:Magnetic Resonance Imaging; D009777:Occipital Bone / Q000033:anatomy & histology / Q000196:embryology; D010012:Osteogenesis / Q000502:physiology*; D011247:Pregnancy; D025341:Principal Component Analysis; D012886:Skull / Q000033:anatomy & histology / Q000196:embryology; D019291:Skull Base / Q000033:anatomy & histology / Q000196:embryology*; D013100:Sphenoid Bone / Q000033:anatomy & histology / Q000196:embryology