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Dissection of Frog (Practical)

Demonstration of Viscera and Identification of Visceral Organs of Frog:


Viscera means the internal body organs and the body cavity is known as visceral cavity. In Frog, the viscera encloses the following organs.


Heart: A reddish muscular organ found at the level of the pectoral girdle in the middle line.


Lung: A pair of spongy, pinkish-white coloured structures found one on each side of the heart.


Liver: A large, reddish brown, bilobed gland found close to the heart and lungs.


Gall Bladder: A small spherical, deep blue structure found between the liver lobes.


Stomach: Large, elongated sac like, white coloured structure. It is divided into an upper cardiac and a lower pyloric stomach.


Intestine (Ileum): The stomach leads into the coiled part of the alimentary canal is the small intestine or ileum.


Rectum: Black coloured tube like large intestine which is the last part of the alimentary canal.


Kidneys: A pair of ,oval brown coloured bodies placed posteriorly dorsal to the alimentary canal.


Pancreas: A large creamy white gland found between the stomach and the duodenum (the first part of the intestine).


Spleen: A small reddish brown spherical body found under the coils of the intestine


Urinary Bladder: A bibbed thin walled bladder found at the pelvic region.


Gonads: In male, a pair of bean shaped yellowish bodies called testes found just above the kidneys. In female, a pair of large, folded, membranous dark bodies with numerous white dot like structures- the ovaries.


Fat bodies: In both male and female frogs clusters of fat bodies are seen attached to the anterior end of their gonads.


Anterior abdominal vein: A vein lying along the midventral line in the viscera.

Frog: Dissection of Digestive System:

Procedure


Take an anesthetised frog and lay it on a dissection board with its ventral surface upwards. Stretch the limbs and pin on the tip of them and also on the snout. Lift the skin in the middle of the abdomen using forceps and cut transversely with the scissors. Make the cut longitudinally upto the tip of the lower jaw. Now lift the skin with the forceps and separate it from the body wall. Pinup the skin to both sides.


Then cut the body-wall through the mid-ventral line. After posing exposing the viscera, remove the organs such as heart, lungs ,kidneys, spleen, gonads, fat bodies, and the anterior abdominal vein.


Now uncoil the alimentary canal with forceps and needle. Then, cut the lower jaw through its base and pin it on a black paper to the other side. Stretch the tongue anteriorly and pin it also. Then, bisect the pelvic girdle with a scalpel or bone cutter to show the cloaca and stretch out the limbs.


Now, extend the alimentary canal to one side and display the dissection by placing black paper strips under the whole length of the gut and the glands.


The alimentary canal of Frog has the following parts:-


Mouth: At the front of the head, there is a wide semicircular opening. The upper and lower jaws form a shield around the mouth.


Buccal Cavity : Mouth leads to a spacious chamber, the buccal cavity in which a fleshy bifid tongue is seen on the floor. The roof of the cavity posses a set of vomer bones with fine vomerine teeth.


Pharynx: Narrow posterior part of the buccal cavity. Communicating with the pharynx are the following openings:


Gullet: this is an opening to oesophagus


Glottis: This is an opening to trachea


A pair of Eustachian: This openings to the middle ear.


Oesophagus: A short, narrow muscular tube.


Stomach: Large elongated muscular sac like structure found dorsal to the liver. Stomach has two Parts:- anterior broad cardiac stomach and posterior tubular pyloric stomach.


Small Intestine: A long coiled tube followed by the stomach. It has two zones- an anterior duodenum and a posterior coiled ileum. Between the stomach and the duodenum, a creamy white gland called pancreas is seen.


Rectum: The last part of the intestine which is almost black coloured. The rectum opens out by the cloacal aperture.


The major digestive gland of Frog is the liver which is a bilobed reddish brown gland found at the level of the stomach. It has a duct called bileduct which opens into the duodenum. The gall bladder is found in the middle of liver lobes.

Figure: Digestive System of Frog

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