Those of the female system are the ovaries, oviducts, uteri, and cloaca. The organs of the male reproductive system are the testes, sperm ducts, and cloac a. Connected to each kidney is a ureter, a tube through which urine passes into the urinary bladder, a sac that stores urine until it passes out of the body through the cloaca. The kidneys are organs that excrete urine. The urinary system consists of the frog’s kidneys, ureters, bladder, and cloaca. Blood from both atria goes into the ventricle and then is pumped into the arteries, which are blood vessels that carry blood away from the heart. Veins from different parts of the body enter the right and left atria. Blood is carried to the heart in vessels called veins. 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. 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. 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.
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