(A) Wild type, hematoxylin and eosin staining of a sagittal section. (B,C) Wild type, coronal sections. (D) Twsg1−/− newborn, sagittal section. Absence of the mandible (m), anterior 2/3 of the tongue (t), underdeveloped nasal (n) and oral (o) cavities, hypoplastic pharynx (ph), lack of connection between the oral cavity and the pharynx in the mutants, but preservation of the hyoid bone (h) (BA2 derivative) in the mutants. (E,F) Twsg1−/− newborn, coronal sections. Absence of the mandible (m), tongue (t), upper incisors (ui), lower incisors (li), mandibular molars (mdm), and nasal septum (ns) in the mutants. Preservation of maxillary molars (mxm) in the mutants. Dashed lines with corresponding letters indicate the level of sectioning. Scale bar: 0.5 mm.