Fig. 2

Pelvic fin development in Scyliorhinus canicula. Developmental stages (St.) at the top. a Scan electron microscopy (SEM) and Mallory’s trichrome stains of histological transversal sections showing initial pelvic fin outgrowth (Pel), laterally to the prospective cloaca region (Cl). b-f SEMs showing the progression of pelvic fin development (ventral views). Note formation of the apical ectodermal fold (AEF) at stage 26 and separation of a proximal domain in which the endoskeleton differentiates (End) and a distal domain, the finfold (Ff) by stage 32. g-k Muscle development between stages 28 and 33 shown with Mallory’s trichrome stains (g, i, k) and MyHC antibody stain (H,J). g Muscle projections entering the fin territory (arrows). h Abductor muscles observed ventrally (Abd). i Abductor and adductor superficialis (Add) muscles detected ventrally and dorsally, respectively. j Dorsal view showing adductor muscles detected from the proximal part of the fin to the distal border of the endoskeleton domain (End), but not in the finfold (Ff). k Chondrogenesis is close to completion, with the pelvic girdle (Grd) clearly detected proximally and prominent abductor and adductor muscles