Fig. 4. Scanning electron micrographs of the fracture surfaces of torn nail clippings, with the main fracture surface running in the transverse direction. (A) In the central area of the nail, fracture follows the orientation of the keratin fibres within the thick intermediate layer. Fracture through the plate-like cells of the dorsal and ventral layers is more jagged. (B) Towards the edge of the nail (left), the failure through the dorsal layer often moves more proximally as it peels off the intermediate layer. (C) A close up of the plate-like dorsal layer and fibrous intermediate layer. (D) Lateral edge of the nail cut with scissors. The dorsal and ventral layers get thicker towards the edge and wrap around the end of the intermediate layer, helping prevent cracks forming. Scale bars, 200 µm (A,B), 100 µm (C,D).