Oral administration of 400 mg/kg of 13-cis retinoic acid to 9 day pregnant mice 
gives rise to important maxillofacial malformations. The first manifestation of 
teratogenic effect is an increase of density of cell death arising in the dorsal 
part of the first two branchial arches at day 9.5. These two arches become 
hypoplastic at days 10 and 11, and the preskeletal anlagen appear too late in 
comparison to control embryos. Meckel's cartilage is too curvilinear and 
medially situated. Pre-ossicular and pre-mandibular blastemata develop with 
spatial distortions which are well analyzable at days 16 and 17. They give some 
arguments to discuss several features of normal early development of this area.