Assertion: vein | /r/HasAspect | thick outer layer
Facets:
value: below this
type: LOCATION
value: microscopically
type: MANNER
Source sentences:
text: Microscopically, veins have a thick outer layer made of connective tissue, called the tunica externa or tunica adventitia.
text: Veins have a thick outer layer made of collagen and below this are thin bands of smooth muscle and elastic tissue, with the innermost layer being made up of endothelium cells.