- It is concerned with the process of nutrition, which includes all the changes taking place in food within the alimentary canal from the time it is taken in and is absorbed into the blood and lymph.
- The digestive system consists of the alimentary canal and the digestive glands.
- also read digestive system of frog and fish comparative anatomy
- Rabbit is a herbivorous animal, therefore, its alimentary canal is long, so as to obtain sufficient nourishment from the vegetable matter.
- The alimentary canal is a long, coiled tube of variable diameter.
- It is suspended in the body cavity by the mesentery.
- It consists of mouth, tongue, teeth, bucco-pharyngeal cavity.
- oesophagus, stomach, small intestine, large intestine and anus.
- The mouth is terminal and relatively small, bounded by two movable lips.
- Mouth leads into a large cavity called Bucco-pharyngeal cavity.
- The buccal cavity is a space situated in the head, the roof of which is formed by the palate; floor is formed by the throat and sides by the cheeks.
- There is a partition separating buccal cavity and nasal cavity, it is called palate.
- The anterior half of the palate is called hard palate, while the posterior half is smooth and fleshy and is called soft palate.
- Above the palate lies a respiratory or narial passage.
- It is divided by a nasal septum into two parts above the hard palate, but above the soft palate it is undivided.
- The buccal cavity is separated from the arial passage by the palate, therefore, rabbit retains its food in the mouth for chewing and there is no hindrance in the breathing process.
- In the anterior part of the hard palate there is a pair of openings called nasopalatine canals, which open into nasal or olfactory cavities.
- There is a Jacobson's organ, situated in each naso-palatine canal.
- The function of Jacobson's organ is to recognize different kinds of food.
- The posterior free edge of the soft palate forms pendulous flap called velum palati or uvala.
- Situated on either side of velum palati is a pit, called the tonsil, which is made up of lymphoid and connective tissues.
- Tongue is situated on the floor of the mouth attached along the greater part of its length to the floor of the mouth but having a free rounded tip in front.
- It is a muscular organ and helps manipulating food and mixing it with saliva.
- There are three kinds of papillae, which are small projections, on which taste-buds are situated.
- The ordinary papillae situated on the dorsal surface of the tongue, are called conical or fili form or fungiform.
- In addition to these ordinary papillae, there is a pair of papillae situated on the dorsal surface of the tongue towards its posterior end.
- Each of these papillae is surrounded by a trench-like depression and is called vallate papilla.
- At the sides of the tongue slightly anterior to the vallate papillae are present two oral transversely ridged areas, called foliate papillae.
- Teeth of rabbit are heterodont i.e., they are not alike or similar.
- Secondly, teeth are lodged in rabbit in sockets or alveoli so it is called thecodont dentition. But in frog, teeth are fused with the jaw bones.
- The teeth found in the rabbit are situated only on the edges of the jaws, while the vomerine teeth are absent.
- Teeth found in the rabbit are incisors, premolars and molars.
- Incisors are chesel-shaped and are used for cutting food.
- The premolars and molars are provide with broad ridged crowns and serve to grind the food.
- Molars develop behind the premolars.
- In rabbit, canines are absent and there is a wide space or diastema situated between incisors and grinders.
- The number and arrangement of the teeth may be expressed by a dental formula as follows:
STRUCTURE OF TEETH
- The teeth are formed from both the epidermis and dermis.
- A typical tooth can be divided into three parts.
- The crown, which is visible part of the tooth and projects out from the gum, the neck lying below the crown in the gum, and the root embedded in a socket of the jaw bones.
- The bulk of the tooth is formed by hard dentine.
- Inside the dentine a pulp cavity is found which contains connective tissue, blood vessels and nerves. The pulp cavity is lined by a layer of odontoblast or bone cells.
- The dentine is chemically bone-like and contains many fine canaliculi in which the processes of odontoblasts run.
- The crown is covered by hard, shiny, white enamel, while the roof is covered a bony cement layer. Further, the attachment of teeth on the jaw bones are strengthened by the gum.
- Pharynx is the hinder part of the bucco pharyngeal cavity.
- It is a short passage into which internal nares open above, while the eustachian tubes open on the sides.
- On the floor of the pharynx, situated just behind the base of the tongue is the glottis, which is an opening into the wind-pipe and is guarded by a leaf-like cartilaginous flap, called epiglottis.
- During the process of swallowing food, soft palate is raised to close the internal nostrils and epiglottis covers the glottis.
- Thus, the food is not allowed to enter into the wind - pipe situated dorsal to the oesophagus.
- It is a long, narrow straight muscular but dilatable tube, which passes backwards through the neck and thorax.
- It pierces the diaphragm to open into the stomach which is situated in the abdominal cavity.
- The opening of the oesophagus remains closed except during the act of swallowing food.
- Thus, the process of respiration goes on without any obstruction.
- It is a large, curved sac lying behind the diaphragm slightly towards the-telt in the abdominal cavity.
- The stomach of the rabbit consists of two parts.
- The larger left part called cardiac and the part narrower right is called pyloric.
- Some authors have described that the stomach consists of three parts, a broad-cardiac, the main fundic part or fundus and a pyloric part.
- The opening of the oesophagus in the stomach is provided with a valve called cardiac valve. Similarly, a-pyloric sphincter or pylorus is situated at the end of the pyloric part of the stomach.
- The walls of the stomach are thick and highly muscular while its mucous lining is provided with various gastric glands.
- These are numerous tubular glands which open by the ducts into the gastric pits.
- The gastric glands of cardiac part are cardiac glands, fundic part are fundic glands and that of pyloric part are pyloric glands.
- It is the first part of the small intestine and runs from pylorus up to the hinder end of the abdomen.
- It is a U-shaped duct and receives the bile duct at its origin while it also receives a pancreatic duct in front of its forward turn.
- It is the first longest part of the small intestine.
- It is a narrow and greatly coiled tube. It is about two or three metres in length, but it is greatly coiled and is thus accommodated in a small space.
- The internal lining of the ileum is raised into numerous finger like projections called villi, which increase the absorptive surface.
- The wall of the ileum possesses several microscopic intestinal glands. Distally, ileum is expanded into a rounded sac called the sacculus rotundus, which opens into the caecum.
- The sacculus rotundus has an ileo-caecal valve by which the contents of the ileum reach into the caecum before passing into the colon.
- It is a thin-walled diverticulum, about 50 cm. long, marked externally by spiral constriction, which indicates the presence of a spiral valve, on the inside.
- Distally, caecum ends blindly in a small finger-like process called the vermiform appendix.
- It proceeds from the caecum and consists of two parts: a proximal colon, which is a wide tube, about 45 cm. long with sacculated appearance.
- Second part is distal, narrow rectum, which is about 75 cm. long having beaded appearance due to the presence of pill like faeces and opens to the outside through the anus.
- It is situated on the underside of the tail and is provided with a sphincter muscle.