Nasal pit formation in the hamster: A transmission and scanning electron microscopic study

Abstract

The surface morphology of cells comprising the nasal placode and adjacent body surface was examined by transmission and scanning electron microscopy during nasal pit formation in hamster embryos ranging in age from 8 1 4 to 9 1 2 days post coitum. A sharp distinction between the apical surface appearance of cells of the nasal epithelium and cells of the surrounding periderm develops at the periphery of the nasal placode. Periderm cells increase in surface area, exhibit a change in the distribution of surface microvilli, and many acquire a single cilium per cell. Cells of the nasal placode retain a dense surface coat of microvilli and exhibit relatively smaller apical surface areas. Olfactory rods can be positively identified on the basis of their ultrastructure at the nasal groove stage. The ventral margin of the nasal groove does not initially depend on the maxillary process, but is bounded by the lateral and medial nasal processes. From their earliest development the oral and nasal cavities appear to be separated in this species.