Fig. 9. Ectopic muscles formed by grafted trunk mesoderm. (A) A large mesenchymal aggregate dorsal to the isthmus is shown; note that myosin is synthesized primarily in abaxial cells (stage 29 embryo, segmental plate graft). This ectopic condensation has not disrupted the emergence of trochlear nerve fibers (n. IV) from the roof of the isthmus. (B) Multiple finger-like projections of ectopic muscle extend ventrally from the isthmus (stage 29 embryo, medial half somite graft). (C,D) Multiple small, ectopic muscle clusters are dispersed along a band deep to and paralleling the dorsal margin of the eye; the edge of the pigmented retina is visible. (E) An ectopic muscle adjacent to the dorsal rectus muscle; there is no mixing between them. Labels: MyHC is purple in A-C and red in D,E; quail nuclei are brown in A-C and black in D,E.