villus a: 1 muscularis mucosae, 2 central lacteal, 3 mucous membrane, 4 capillary network, 5 circular muscle, 6 longitudinal muscle, 7 serosa, 8 submucosa, 9 lymphatic vessel, 10 muscular coat, 11 submucosa, 12 epithelial cell, 13 arteriole, 14 venule, 15 villus