<Tr> <Th> Layer </Th> <Th> Duodenum </Th> <Th> Jejunum </Th> <Th> Ileum </Th> </Tr> <Tr> <Td> Serosa </Td> <Td> 1st part serosa, 2nd--4th adventitia </Td> <Td> Normal </Td> <Td> Normal </Td> </Tr> <Tr> <Td> Muscularis externa </Td> <Td> Longitudinal and circular layers, with Auerbach's (myenteric) plexus in between </Td> <Td> Same as duodenum </Td> <Td> Same as duodenum </Td> </Tr> <Tr> <Td> Submucosa </Td> <Td> Brunner's glands and Meissner's (submucosal) plexus </Td> <Td> No BG </Td> <Td> No BG </Td> </Tr>

Where is the lumen in the small intestine