Important Tips Cellulose is digested by the enzyme cellulase synthesized by the microorganisms present in the lumen. Cellulose Acetic acid + Propionic acid + Butyric acid + Small chain fatty acid. Sacculus rotundus is a dilated sac like structure present in rabbit at the junction of ileum, caecum and colon. It contains ileo-caecal valve, which guides the direction of food from ileum to caecum. Sacculus rotundus is absent in human but ileo-caecal valve is present. The hindgut of all vertebrates (except metatherian and eutherian mammals) includes cloaca and cloacal aperture, instead of anal canal and anus. Cloaca is divided into three parts(i) Coprodaeum is a part of rectum, where faeces are stored.(ii) Urodaeum a depression in the part of cloaca where urinary duct and urinary bladder open.(iii) Proctodaeum terminal part of cloaca that is common opening for the excretion of urinary, genital and faecal matter and externally open by anus. Digestion of cellulose takes place in caecum of rabbit with the help of enzyme cellulase produced by symbiotic microorganism. Cellulose digestion does not occur in human. Peyers patches in the intestine are the site of production of B-lymphocyte. In most of the vertebrate's protein digestion ends in ileum. The study of alimentary canal is called Enterology. Auerbachs plexus is present in small intestine. Digestion of cellulose is also found in termites (white ants). In which symbiotic flagellate Triconympha found in their intestine that secretes enzyme -glucosidaes which hydrolyse the cellulose to sugars which are used by both symbionts. Bursa fabricus is also called cloacal thymus, is a lymphoid mass in the cloaca of birds. It is site of differentiation of B-lymphocytes. So a part of immune system.