Fig. 3

The development of the amniote jaw complex involves critical contributions from multiple embryonic populations. a Frontal view of stage 25 quail embryo. The frontonasal (fn), maxillary (mx), and mandibular (ma) primordial are visible (dotted line indicates the sagittal section plane for b). b By stage 25, the frontonasal (fn), maxillary (mx), mandibular (ma), and hyoid (hy) primordia (sagittal view) are populated by NCM (light blue) surrounded by surface ectoderm (se; tan), pharyngeal endoderm (pe; yellow), and forebrain neuroepithelium (fb; dark blue) and contain contributions from neural crest, nasal placode (np), and cranial ganglia (V, VII, IX). Mesoderm (m) that produces skeletal tissues is distributed caudally. c Prior to migration, at stage 9.5 (dorsal view) cranial NCM (light blue) delaminates from the forebrain (fb), midbrain (mb), and hindbrain rhombomeres (r; dark blue). Cranial NCM migrates alongside paraxial mesoderm (m; orange). d, e Head skeleton of adult quail and duck. The duck surangular bone, which lies dorsal to the dentary bone along the lower jaw (inset), contains a robust coronoid process (black arrow) along its lateral margin that is absent in quail. f, g The mandibular adductor muscles (white dashed outline), which close the jaw, are relatively larger in ducks than in quails. The caudal external mandibular adductor muscle originates posterior to the orbit and inserts laterally on the duck coronoid process (black arrow). This muscle is relatively smaller in quails and inserts along the dorsal margin of the surangular. h By stage 38 in quails, the narrow mandibular adductor muscle (orange) inserts dorsally onto the coronoid process of the surangular bone (light blue). i By stage 38 in ducks, the broad mandibular adductor inserts laterally onto the coronoid process and contains a secondary cartilage (arrow) within the tendon enthesis