sheath

名词 sheath:

1. a protective covering for a knife or sword
2. an enveloping structure or covering enclosing an animal or plant organ or part
   同义词：case
3. a dress suitable for formal occasions
   同义词：cocktail dress

1. The sheath of connective tissue enclosing a bundle of nerve fibers.
   经来膜包裹住神经纤维的膜状结缔组织
2. A growing feather still enclosed in its horny sheath, especially one just emerging through the skin.
   (鸟类的)新生毛一种裹在角鞘中的新生毛，特别是刚刚冒出皮肤外的羽毛
3. The innermost layer of the cortex that forms a sheath around the vascular tissue of roots and some stems.
   内皮层皮层的最内层，在根、茎的导管组织周围形成一道叶鞘(茎衣)