The prenatal development of the human nasal and vomeral bones.

The purpose of the present study was to establish normal prenatal development standards for the nasal and vomeral bones, both formed by intramembranous ossification in the membrane covering the cartilaginous nasal capsule. The study is based upon a combination of macroscopic (devisceration and radiography) and microscopic (histology) analyses on 62 normal human fetuses from spontaneous and induced abortions, ranging in gestational age from 9 to 24 weeks, representing crown-rump lengths (CRL) from 33 to 225 mm. Special attention was paid to the onset of bone formation in relation to other maturity aspects and to the growth of the bones. The very first onset of ossification of the vomeral bone is observed as two bilateral ossification centers, prior to nasal bone ossification. Later, the two bilateral ossification centers fuse caudally below the cartilaginous nasal septum, thus changing into a U-shaped bone when observed in the coronal plane. By bony apposition caudally the U-shaped vomer gradually changes into a Y-shape. The nasal bone appears as a thin bony contour ventral to the cartilaginous nasal septum in the sagittal plane, and changes gradually during growth to a wedge-shaped bone. Knowledge of the early development of the internal nose (vomeral bone) and external nose (nasal bone) is significant in understanding mid-face congenital malformations.