ELECTRON MICROSCOPY: VESSELS: VASCULAR: CARDIOVASCULAR: VESSEL: Capillary, fenestrated. (EM-labeled); RCH/Prospect6356, sheep rumen, mucosal capillary. 1-lumen of capillary, 2-capillary fenestration with diaphragm, 3-basal lamina of ruminal (lining, mucosal) epithelium, 4-mitochondrion with a large matrix granule