capsula
noun [ C ] anatomy specialized uk/ˈkæp.sjə.lə/ us/ˈkæp.sə.lə/ capsulae /ˈkæp.sjə.liː/ /ˈkæp.sjə.liː/ (also capsule)
（包围器官、关节或其他结构的）囊，被膜
a flexible (= not stiff or fixed) structure surrounding an organ, joint, or other structure in the body