umbilication
  臍形渦
  um·bil·i·ca·tion /ˌəmˌbɪləˈkeʃən/ 名詞
  成臍形,凹陷
  Um·bil·i·ca·tion n. A slight, navel-like depression, or dimpling, of the center of a rounded body; as, the umbilication of a smallpox vesicle; also, the condition of being umbilicated.
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