Fig. 3

Myogenesis and chondrogenesis at segmental and post-segmental pharyngeal stages (a) MYOD expression in a HH21 chick embryo. Myogenesis can be seen to be occurring in the first two arches but not the more posterior arches. The migratory hypoglossal myoblasts, which are somite derived can be seen to migrate through the ventral pharyngeal midline region – white arrow. b MyoD expression in a TS16 mouse embryo. Myogenesis can be seen to be occurring in the first two arches, but not the more posterior arches. The somite derived hypoglossal myoblasts can be seen to be migrating around the caudal aspect of the pharyngeal arches and along the ventral pharyngeal midline, indicated by the white arrow. c MYOD expression in chick embryo at HH25. Ongoing myogenesis can be seen to be occurring in the somites and within the limb buds. There is some myogenesis apparent in the extended second pharyngeal arch, but not in the posterior pharynx. d Longitudinal section through the pharyngeal region of a HH25 chick embryo. MYOD expression within the second arch is apparent, but there is no expression in the more posterior pharyngeal region. MYOD expression is also seen in the somites. The position of the notochord (N) is marked. e MyoD expression in mouse TS17 embryo. Myogenesis is associated with the somites, developing limb buds and anterior pharyngeal arches, but is absent from the posterior pharyngeal region, except for expression in the hypoglossal myoblasts, indicated by the white arrow. f COL2A expression in HH25 chick embryo. Ongoing chondrogenesis can be seen to be occurring in the somites and limb buds. There is some chondrogenesis apparent in the extended second pharyngeal arch but not in the posterior pharynx. g Longitudinal section through the pharyngeal region of a chick embryo at HH25. COL2A expression within the second arch is apparent, as is expression around the notochord (N) but there is no expression in the more posterior pharyngeal region. h Col2a expression in mouse TS17 embryo. Chondrogenesis is associated with the somites, developing limb buds and anterior pharyngeal arches, but is absent from the posterior pharyngeal region