Abomasum refers to the fourth stomach of a ruminant or grass-eating animal, e.g. a cow which receives food from the omasum and passes it to the small intestine. In it, the main work of digestion is done.
Omasum ↑ refers to the third stomach of a ruminant or grass-eating animal which located between the reticulum and the abomasum.
Reticulum ↑ refers to the second stomach of a ruminant or grass-eating animal, having a honeycomb like structure, receiving food from the rumen and passing it to the omasum.
Rumen ↑ refers to the first stomach of a ruminant or grass-eating animal, which receives food or cud from the esophagus, partly digests it with the aid of bacteria, and passes it to the reticulum.
Esophagus is the part of the alimentary canal that connects the throat to the stomach. Food enters the mouth and travels through the esophagus to the stomach especially in Rumen.
Intestine is the lower part of the alimentary canal from the end of the stomach especially abomasum to the anus.
Small Intestine is the part of the intestine that runs between the stomach especially abomasum and the large intestine;
Reference: An Elementary Scientific and Technical Dictionary
What is Abomasum? What is omasum? What is Reticulum? What is Rumen