Look for the opening to the frog’s cloaca, located between the hind legs.Use a probe to help find each part: the vomerine teeth, the maxillary teeth, the internal nares, the tongue, the openings to the Eustachian tubes, the esophagus, the pharynx, and the slit-like glottis. Use the diagram below to locate and identify the structures inside the mouth. Cut the hinges of the mouth and open it wide. Turn the frog on its back and pin down the legs.Find the mouth, external nares, tympani, eyes, and nictitating membranes. Use the diagram below to locate and identify the external features of the head.Observe several frogs to see the difference between males and females. Male frogs are also usually smaller than female frogs. A male frog usually has thick pads on its “thumbs,” which is one external difference between the sexes, as shown in the diagram below.
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To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs.
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The heart has two receiving chambers, or atria, and one sending chamber, or ventricle. The circulatory system consists of the heart, blood vessels, and blood. The walls of the lungs are filled with capillaries, which are microscopic blood vessels through which materials pass into and out of the blood. The respiratory system consists of the nostrils and the larynx, which opens into two lungs, hollow sacs with thin walls.
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Indigestible materials pass through the large intestine and then into the cloaca, the common exit chamber of the digestive, excretory, and reproductive systems. The contents of the common bile duct flow into the small intestine, where most of the digestion and absorption of food into the bloodstream takes place.
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Bile flows into a tube called the common bile duct, into which pancreatic juice, a digestive juice from the pancreas, also flows. Bile is a digestive juice made by the liver and stored in the gallbladder. From the esophagus, swallowed food moves into the stomach and then into the small intestine. The digestive system consists of the organs of the digestive tract, or food tube, and the digestive glands. In the pharynx, there are several openings: one into the esophagus, the tube into which food is swallowed one into the glottis, through which air enters the larynx, or voice box and two into the Eustachian tubes, which connect the pharynx to the ear. Also inside the mouth behind the tongue is the pharynx, or throat. Inside the mouth are two internal nares, or openings into the nostrils two vomerine teeth in the middle of the roof of the mouth and two maxillary teeth at the sides of the mouth. The third lid, called the nictitating membrane, is transparent. On the outside of the frog’s head are two external nares, or nostrils two tympani, or eardrums and two eyes, each of which has three lids. As members of the class Amphibia, frogs may live some of their adult lives on land, but they must return to water to reproduce.