The hindgut of the avian digestive system terminates in the cloaca. The external opening through which faecal matter and uric acid is excreted is called the vent. The shape of the vent varies depending on species. | The hindgut of the avian digestive system terminates in the cloaca. The external opening through which faecal matter and uric acid is excreted is called the vent. The shape of the vent varies depending on species. |