Caecum is a small blind sac which is harbouring some symbiotic micro-organisms e.g. E.coli. The caecum opens into the colon.
The innermost layer lining the lumen of the alimentary canal is the mucosa. This layer forms irregular folds (rugae) in the stomach and small finger-like foldings called villi in the small intestine. The cells lining the villi produce numerous microscopic projections called microvilli giving a brush border appearance. 
The tongue is a freely movable muscular organ attached to the floor of the oral cavity by the frenulum. The upper surface of the tongue has small projections called papillae, some of which bear taste buds.
The opening of the stomach into the duodenum is guarded by the pyloric sphincter.