Rabbit: external features, digestive system and dentition
The rabbit is a herbivorous mammal with fur, whiskers and long ears. Its gnawing incisors, a gap called the diastema, and a large caecum suit a diet of plants.
External features
| Part | Features |
|---|---|
| Body covering | Soft fur (hair); the body is divided into head, neck, trunk and tail |
| Head | Mouth with a cleft (split) upper lip. Long, touch-sensitive whiskers (vibrissae), a pair of nostrils, and large eyes with eyelids and a nictitating membrane. Long, movable external ears (pinnae) |
| Neck | Short; lets the head turn |
| Trunk | Front thorax and hind abdomen. Forelimbs are short and hindlimbs are long (for jumping); every digit ends in a claw. Females have mammary glands with teats |
| Tail | Short and bushy; the anus and the urinogenital opening lie below it |
Alimentary canal and digestive glands
The caecum is a large, thin-walled sac; the **vermiform appendix** is its finger-like tip. Rabbits eat their soft night droppings (**coprophagy**) to absorb the vitamins made by caecal bacteria.
Dentition
- The teeth sit in sockets of the jaw bones: thecodont.
- There are two sets in life, milk teeth and permanent teeth: diphyodont.
- There are different kinds of teeth (incisors, premolars and molars): heterodont.
- Incisors are chisel-like and grow throughout life. Enamel only on the front face keeps them sharp for gnawing. The upper jaw has two pairs: a large pair and a small, peg-like pair behind it.
- There are no canines. The toothless gap between the incisors and premolars is the diastema; it lets the tongue move food from the front to the grinding teeth.
- Premolars and molars have broad, ridged surfaces for grinding grass and leaves.
Count the teeth from the dental formula
The dental formula of the rabbit is I 2/1, C 0/0, PM 3/2, M 3/3. Find the total number of teeth.
- The formula shows one half of each jaw (one side of the mouth).
- Upper half-jaw: 2 + 0 + 3 + 3 = 8 teeth
- Lower half-jaw: 1 + 0 + 2 + 3 = 6 teeth
- One side of the mouth: 8 + 6 = 14 teeth
- Both sides: 14 × 2 = 28 teeth
The rabbit has 28 teeth. (An adult human has I 2/2, C 1/1, PM 2/2, M 3/3 = 32.)
How to draw the digestive system of a rabbit
- 1Draw a thin tube, the oesophagus, coming down into a bean-shaped stomach on the left.
- 2From the stomach, draw a U-shaped loop: the duodenum. Draw the liver with a gall bladder above it and the pancreas inside the loop, with ducts joining the duodenum.
- 3Continue as a long, coiled ileum ending in a small round swelling: the sacculus rotundus.
- 4Draw a large, coiled, sac-like caecum with a thin, finger-like tip: the vermiform appendix.
- 5From the caecum, draw the colon, then a beaded rectum with pellets, ending at the anus.
Rabbits and squirrels gnaw, and their ever-growing incisors must be worn down, so pet rabbits need hay or twigs to chew. Like cattle, rabbits depend on gut bacteria to digest the cellulose in grass and leaves.
2 marks: “Write the dental formula of the rabbit. What is the diastema?” I 2/1, C 0/0, PM 3/2, M 3/3 = 28. The diastema is the gap between the incisors and premolars, as canines are absent.
4 marks: “Why is the dentition of the rabbit called thecodont, diphyodont and heterodont?” Teeth sit in jaw sockets (thecodont); two sets grow in life (diphyodont); there are different kinds of teeth (heterodont). Add the dental formula and diastema.
7 marks: “Describe the digestive system of the rabbit with a labelled diagram.” Labelled diagram; parts from mouth to anus with sacculus rotundus, caecum and appendix; glands (salivary, gastric, liver, pancreas, intestinal); cellulose digestion in the caecum; dentition.
Rabbit teeth: '2-0-3-3 over 1-0-2-3', total 28. 'The Dentist Helps': Thecodont, Diphyodont, Heterodont.