Fig. 7. Continuing development of the epaxial musculature. (A) A composite of four consecutive z-scans through the plane of the myotome of an E4 embryo transplanted at ssXV at 20 somites with the ssXIV DML of a 21-somite quail embryo. Extensive dorsomedial expansion of quail myotome is evident (bar) and a dense cluster of quail nuclei are located at the DML position. The myotome has retained its uni-segmental organisation and central myocyte nuclei alignment. Some quail dermis cells (arrowheads) are present over the neighbouring somite and at the caudal edge of the transplanted somite. (B) Dorsal view of desmin immunoreactivity composite of a z-series through an embryo that received a DML transplant of ssX at 20 somites with a ssXV DML from a 25 somite quail and was re-incubated for 5 days. Broken bars mark, and join, corresponding neighbouring segments. The unbroken bar joins the transplanted segment (asterisk) to its contralateral counterpart. Medially, the musculature is unisegmental while the overlying more laterally positioned muscle extends over several segments. Arrowheads indicate more intensive immunolabelling at the medial limit of the musculature. (C) A higher magnification view of the medial limit of the transplanted segment. Quail nuclei are evident within myofibres (arrows). bv, blood vessels.