With the emergence of mammals, the digestive system was modified in a variety of ways depending on the animal's diet. For example, the cat has simple large intestines, while the horse has a voluminous large intestine. Animals utilize different diets. Accordingly, their digestive tracts are different. The digestive system includes the alimentary canal (a tube that extends from the mouth to the anus), oral structures (lips, teeth, tongue) and accessory digestive glands (salivary gland, liver, and pancreas). In addition to oral structures, the principal parts of the digestive system are pharynx, esophagus, stomach, small intestines, and large intestines. Many of these structures have evolved very little since the earliest fishes.

The major function of the digestive system is to provide nutrients to the body tissues. This involves: Ingestion of food; chewing; swallowing ; secretion of enzymes, acids, buffers, and bile), movement and mixing of food; absorption, and getting rid of the waste products

Mechanical and chemical digestion ...

Digestion involves mechanical and chemical activities. The mechanical part of digestion involves tearing, grinding and mixing food with enzymes. Chemical digestion is done by various digestive enzymes.

Oral Cavity

The oral cavity is responsible for the grasping and ingestion of food, grinding of food, moistening and lubrication, and formation of food boluses that are then plunged into the pharynx for swallowing. The structures of the oral cavity include lips, cheeks, teeth, tongue, palate, and salivary glands.

Secondary Palate

evolution of the secondary palate allows for dual mastication and breathing. The hard palate separates the nasal passages from the mouth. This first appears in reptiles and further evolves into the mammalian secondary palate.