Anatomy videos for medical students

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Mammoth Cave is located in Mammoth Cave National Park in Kentucky, USA. It is considered the world’s longest cave system known. This UNESCO World Heritage Site’s official name is Mammoth-Flint Ridge Cave System for the ridge under which the cave has formed. It was also declared a Biosphere Reserve in 1990. It consists of more than 630 km of passageways and is almost thrice as long as the second longest cave system.

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Jewel Cave, which is part of Jewel Cave National Monument, is currently the world’s second longest cave with 243.56 km of mapped passageways. This popular cave is located in Black Hills, South Dakota. It was discovered in 1900.

Optymistychna is a cave in Ukraine. The meaning of the name is "optimistic". It is the world’s third longest cave with 230 km of mapped passageways as of 2005. It is the largest cave complex in Eurasia. It also holds the distinction as the world’s longest gypsum cave. This fascinating cave won the special nomination as the National Wonder of Ukraine in 2008.

Ox Bel Ha which means "Three Paths of Water" is officially known as Sistema Ox Bel Ha. This cave system is located in Quintana Roo, Mexico and is the world’s longest explored underwater cave and is rank number 4 including dry caves. Its length as of May 2011 is surveyed at 222.3 kilometers of underwater passages.

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Sistema Sac Actun is a unique underground river in Mexico. It means "White Cave System" in English. This underwater cave system is situated along the Caribbean coast of the Yucatan Peninsula. It is presently regarded as the second longest underground river in the world. It is the second longest surveyed cave system in Mexico and the 6^th longest in the world. As of January 2011, this cave system currently measures 215.4 kilometers. 

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Lechuguilla Cave is the 6^th longest cave in the world with a length of 210 km as of June 2011. It is located in Carlsbad Caverns National Park in New Mexico, USA. The cave is also the deepest cave in mainland USA with a depth of 489 meters. The cave is well-known for its peculiar geology, rare formations and pristine condition. Its name was taken from Agave lechuguilla, a plant species that grows near its entrance.

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Wind Cave is part of Wind Cave National Park located in the town of Hot Springs in South Dakota, USA. Wind Cave is notable for its displays of the calcite formation known as boxwork and is also known for its frostwork. The cave is also considered a three-dimensional maze cave, recognized as the densest (most passage volume per mi³) cave system in the world. The caves current length is 210.89 km, with an average of four new miles of cave being discovered each year. Above ground, the park includes the largest remaining natural mixed-grass prairie in the United States.

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Holloch Cave is previously known as the world’s largest cave complex until the discovery of Mammoth Cave in 1970. This cave is 197 kilometers in length and is located in the Valley of Muotha in Switzerland. It is the second longest European cave and is also notable for having a depth of 939 meters.

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Fisher Ridge Cave System is 180 kilometers in length and it is located near Cave City in the state of Kentucky, USA. It is part of the Mammoth Cave National Park. The cave is a popular tourist destination.

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Gua Air Jernih is a 174 kilometers long cave located in Miri, Sarawak in Borneo, Malaysia. It was explored in 1978 and is part of Gunung Mulu national Park. This show cave was declared a UNESCO World Heritage Site.

Ozernaya Cave with a length of 122 kilometers is the 11^th-longest cave in the world. It is located in Ukraine.