The human body contains about 640 muscles, the largest of which (by volume) is the Gluteus Maximus, otherwise known as the buttocks. These are used for hip extension and hip external rotation and can be trained with squats, deadlifts and lunges.
The longest muscles however are the Sartorious muscles in the upper legs, running from the upper thigh down to the inside of the knee. These are used to flex and rotate the legs.
Parts of the body are usually given latin names as this has been the formal language of study and science since the Middle Ages, used by the Roman Catholic Church. Gluteus Maximus muscle translates as 'largest buttock' muscle (there are other muscles in the buttocks), and Sartorious translates as 'tailor's muscle' since these muscles enable sitting in the cross-legged position in which tailors traditionally sat whilst sewing.
The Gluteus Maximus, one of three gluteal muscles, is located at the back of the hip and is commonly called the buttocks. It’s main functions are hip extension and hip external rotation. Some great exercises to train the Gluteus Maximus muscles include squats, deadlifts and lunges.