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The reticulorumen represents the first chamber in the alimentary canal of ruminant animals. It is composed of the rumen and reticulum. The reticulum differs from the rumen with regard to the texture of its lining. The rumen wall is covered in small, finger-like projections called papillae, which are flattened, approximately 0.5 cm in length and 0.3 cm wide in cattle. The reticulum is lined with ridges that form a hexagonal honeycomb pattern. The ridges are approximately 0.1–0.2 mm wide and are raised 0.5 cm above the reticulum wall. The hexagons in the reticulum are approximately 2–5 cm wide in cattle. Despite the differences in the texture of the lining of the two parts of the reticulorumen, it represents one functional space. Microbarial fermentation degrades ingested carbohydrates in the reticulorumen to the volatile fatty acids acetate, propionate and butyrate, and proteins to short peptides, amino acids and ammonia. This fermentation is anaerobic, and allows the microbes in the reticulorumen to derive the energy and amino nitrogen for growth and reproduction. Ruminants absorb the volatile fatty acids across the reticulorumen wall and use them for energy, while the microbes eventually flow out of the rumen into the remainder of the alimentary canal, where they are eventually digested and absorbed. The reticulum, at approximately 5–20 litres, is considerably smaller in capacity than the rumen, which is approximately 100–200 litres in cattle. The oesophageal groove, which links the oesophagus and the omasum, is located in the reticulum.