FACIAL AND VISCERAL ARCH DEVELOPMENT IN MOUSE EMBRYO - STUDY BY SCANNING ELECTRON-MICROSCOPY

Abstract

The external features of face and neck development during the days 8-13 of growth of CD-1 strain mice were studied by scanning electron microscopy of glutaraldehyde-fixed and critical point dried embryos. After the cervical fold was formed (stage 12) the mandibular primordium appeared (stage 13) followed by the primordia of arches II and III (stage 14) with arch IV forming last (stage 15). Arches II, III and IV regressed in reverse order, with no evidence that a cervical sinus pouch was formed. Placodes of the sensory ganglia from cranial nerves 7, 9 and 10 were formed in the 1st, 2nd and 3rd visceral grooves, respectively. Formation of the external auditory meatus and its surrounding tubercles were also observed. Morphogenesis of the upper face was dominated by the midsagittal groove, which extended into the stomatodeum and by the medial nasal, lateral nasal and maxillary processes. The temporal changes in shape and the interrelationships of the structures mentioned were described.