Figure 2: Comparison of histological structure of the superficial BHC (a) and the umbilicus tissue (b), (c) in rabbits. (a) Profile of BHC reported by Professor Kim (J Jo Sun Med, vol. 90, 1963 pages 6–35). (b) BHC-like structure of the young rabbit’s umbilicus found by Chinese researchers in 1964 (an original photo unpublished) ( ). (c) Partial components of the umbilicus (c) stained with H&E method. Both BHC and umbilicus are divided into ectoplasm (composed of smooth muscles, elastic fibers, argyrophilic fibers, etc.) and endoplasm (Endop, containing chromaffin cells, blood vessels, Fibrillenstruktur, etc.) ( ). BHD: Bonghan duct, BHD-L-T: BHD-like tubule; , , : radiation-like smooth muscle; , , : outer-circular layer smooth muscle; , , : entolongitudinal layer smooth muscle; , : chromaffin cells; , , : blood vessels, : Fibrillenstruktur, , : elastic fibers, and h: skeleton muscle.