(A) Summary of Lim HD and Eph/ephrin expression in MNs and limb mesenchyme of tetrapods. (B) In Leucoraja, Foxp1+ LMC neurons segregate into a medial Isl1+ population (LMCm) and lateral Lhx1+ (LMCl) group at fin levels. (C) EphA4 is expressed by lateral (L) LMC neurons, while EphB1 is expressed medially (M). EphA4 is also detected in MMC neurons. (D and E) EphA4 is expressed in dorsal fin mesenchyme, while EphB1 is expressed ventrally. (F and G) Lmx1b is expressed in dorsal fin mesenchyme. (H) Dorsal view of a st29 Leucoraja embryo showing the pectoral and pelvic fins develop adjacent to each other. (I and J) Wholemount immunostaining of NFAP showing axon innervation pattern in the pectoral (I) and pelvic fins (J). (K, L) Vibratome cross-sections of st31 Leucoraja showing axonal projections in the pectoral fin by NFAP staining and dorsal and ventral muscle masses stained with MF20. (M,N) Projections and muscle in the pelvic fin. Panels K–N are composites of tiles made in Zen software. (O) HRP injections in dorsal muscles at st29, showing colocalization with Lhx1. See also Figure S4.