Histological section of regenerating froglet hindlimb at 12 days post-amputation through the mid tibia-fibula. The section is cut through the dorsoventral plane such that the tibia (T) and the accompanying flexor and extensor muscle masses are visible (red). A cartilage collar (CC) has formed around the tibia for some distance proximal to the amputation plane that merges distally with a similar collar surrounding the fibula. A fibroblastema (FB) that will form the cartilage spike is present between the merge point of the cartilage collars and the apical epidermal cap (arrow). Yellow line indicates the plane of tissue harvest.