The lower chamber of the inner ear is called sacculus. It forms a patchy tube like a snail shell. It is called cochlea. Cochlea has 3 chambers. scala vestibuli, scala media and scala tympani. The scala vestibuli is superior and filled with perilymph, the scala media is medial and filled with endolymph, and the scala tympani is inferior and filled with perilymph. The scala media consists of Ressner’s membrane above and Basil’s membrane below. Some epithelial cells above the basilar membrane transform to form the organ of Corti. Organ of Corti is a sensory organ. Organ of Corti contains 5000 sensory neurons. The place where the scala vestibula and scala tympani meet is called the helicotrima.