Shoulder

Brachium

Antebrachium

Facial and Masticatory Muscles

Thorax and Heart

Brain

Body Wall

Hip and Thigh

Shank and Foot

Digestive System

Urinary and Reproductive Systems

Hip and Tail

Digestive system of the Rabbit (Oryctolagus cuniculus)

Photos and Text by Janelle Cooper and Alexandra Sardi

Dissection Notes:

The digestive system of the rabbit was extremely easy to expose and remove.  The rabbit’s abdominal muscles are thin and easy to cut through.  We had to cut through the mesentery attached to the small intestine in order to spread it out. Although somewhat tedious, this was, overall, a simple procedure.  The organs themselves were very easy to remove and we left only the kidneys, which are retroperitoneal and will be discussed in the urogenital lab. 

Description:

At the cranial end of the abdominal cavity, the largest and most ventral structure is the liver.  The liver is the largest organ in the rabbit and is divided into right and left halves. The left half has two lobes, and the right half has three lobes (1).  On the ventro-medial surface of the right median lobe we should have found a small green gallbladder, according to the literature.   It was absent in our rabbit and will be discussed below.    We dissected the hepatic ducts from the liver (there were no cystic ducts) and saw it pass into the duodenum caudal to the pylorus, the junction of the small intestine and stomach.   We also saw the pancreas, which was various streaks of glandular tissue and did not look like a gland.  The rabbit has a single pancreatic duct, called the accessory pancreatic duct, and it opens to the caudal end of the duodenum, separate from the bile duct (2).  The rabbit possesses a greater omentum that extends from the greater curvature of the stomach to the dorsal abdominal wall.  This contains fat deposits and lymph nodes (2).   The rabbit has a huge cecum that will be discussed below.  The colon extends from the cecum to the rectum and is divided into the ascending colon, transverse colon and descending colon in the rabbit (2).  The digestive tract ends in the rectum, anal canal and finally the anus.

Discussion:

The digestive system of the rabbit follows the pattern of that of any other non-ruminant herbivorous animal.  Upon opening the abdominal cavity, we noticed the incredible difference between the comparative sizes of the abdominal and thoracic cavities. The abdominal cavity was huge and filled with the long hindgut.  Furthermore, we found a cecum that was two to three times the size of the stomach.  We had expected the large cecum because the rabbit digests many materials that are high in cellulose, such as grasses, leaves and other vegetation.  Foods that are low in nutritional value, such as vegetation, mandate a large gut capacity (3).  The cecum provides the space, bacteria and enzymes that allow the food to ferment for up to a week so that the cellulose can be converted to absorbable carbohydrates.  In the rabbit, the product from the cecum is excreted and re-ingested through coprophagy (1).  The rabbits produce and re-ingest feces during the night and early morning that come directly from the cecum and these are re-ingested to take advantage of the remaining nutrients.  The feces produced during the day are recycled feces and are never re-ingested.  Coprophagy is extremely important in the rabbit’s ingestion of vitamin K and all B vitamins, amino acids and volatile fatty acids (4).  Prevention of coprophagy leads to severe vitamin deficiencies. 

We did not find a gallbladder in our rabbit.  The literature states that there should be a small one but it was absent in our rabbit or so reduced that it was lost in the dissection.  It makes sense that the gallbladder would be reduced because the rabbit does not eat a lot of fatty foods and the main purpose of the gallbladder is to store bile which is used in the breakdown of lipids.  Animals such as carnivores, on the other hand, may be expected to have a larger gallbladder. 

While the rabbit had a huge cecum and long gut to absorb all the possible nutrients from its low energy food, animals such as the cat had much shorter guts.   The table below compares the different animals we dissected in lab.

The beaver and the rabbit showed classic herbivorous digestive systems with proportionately long large intestines and huge cecae to help break down cellulose.  The cat showed a typical carnivorous digestive system.  The cat did not possess a cecum, as would be expected since it does not break down cellulose.  Its small intestine was comparatively longer and this also makes sense as it usually ingests a large amount of high calorie food and would need the small intestine to quickly expand and absorb all the nutrients.  The large pancreas makes sense as it ingests a lot of calories at a time and can go long periods of time with out ingesting any.  The insulin and glucagons secreted by the pancreas could help regulate these ups and downs (3).  Most omnivores from class had a mid-sized gut.  Rodents also practice coprophagy so we expected the rat to have a cecum.  Its cecum was smaller than the rabbit’s because it also eats other foods and does not subsist entirely on grass and leaves.  The small intestines of the omnivores were proportionately larger which can be expected because when they eat high calorie foods they need to be able to absorb a lot of nutrients quickly. 

References:

1. McLaughlin C.A., Chiasson R.B., Laboratory Anatomy of the Rabbit, McGraw-Hill, New York: 1990.

2. Wingerd, Bruce D., Rabbit Dissection Manual, Johns Hopkins University Press, Baltimore: 1985.

3. Kardong, Kenneth V., Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, New York: 2002.

4. Kent, George C. and Carr, Robert K., Comparative Anatomy of the Vertebrates. McGraw-Hill, New York: 2001.