Fig. 4

Development of the pectoral fin muscles in Neoceratodus forsteri (Australian lungfish) [99]. a Ventral process of the dermomyotome extending ventrally across the pronephric ducts at Stage 42. Note the dermomyotome in N. forsteri is not segregated from the myotome, unlike in amniotes. b Ventral process of the dermomyotome separated from the dorsal dermomyotome at Stage 43+. c Enlarged image of the ventral process of the dermomyotome in (b). At this stage, the migratory muscle precursors (MMPs) are delaminated from the lateral lamina of the ventral process of the dermomyotome, showing a similarity with amniote limb muscle precursor cells. d Dorsal and ventral premuscle masses at Stage 44+. At this stage, individually migrating cells are distributed in the dorsal and ventral parts of the fin bud in N. forsteri, like in amniotes (see Fig. 3). e Dorsal and ventral premuscle masses at Stage 46. f Onset of myofibers of the dorsal and ventral muscles of the pectoral fin at Stage 48. cart, cartilage; coel, coelom; dmt, dermomyotome; dmtv, ventral process of the dermomyotome; dm, dorsal muscle; dpmm, dorsal premuscle mass; int, intestine; mmp, migratory muscle precursor; pcc, precartilage condensation; pl.ompt.post, plexus omopterygius posterior; prn, pronephros; smp, somatopleure; vm, ventral muscle; vpmm, ventral premuscle mass