The digestive system of Rattus norvegicus is constituted by the alimentary canal and the digestive glands (Fig. 1.143).

Digestive system of Rattus

(i) Alimentary Canal:

It is a long tube star­ting from mouth to anus. But the tube is demarked into different regions. The func­tion of each region is different.

(a) Mouth:

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The alimentary canal begins from the mouth. It is a transverse aperture and is guarded by two soft and movable lips. The upper lip is provided with a cleft in the middle.

(b) Buccal cavity:

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Mouth leads to the buccal cavity. The roof of the buccal cavity is formed by a palate. The anterior portion of the palate is called hard palate. The palate separates the mouth cavity from the nasal passage. The floor of the buccal cavity houses the tongue. The anterior end of the tongue is free and the posterior end is attached with the floor.

The tongue is muscular and movable. The upper surface of the tongue is rough and contains numerous papillae or taste buds. Both the jaws are provided with teeth. The teeth help in ingesting food. Teeth are thecodont, heterodont and diphydont type. Dental formula is 1.0.0.3/1.0.0.3. The incisors are long, chisel-shaped and can be seen from outside.

A tooth has two parts, crown and root. Crown is the visible p