The parathyroid glands are four or more small glands, about the size of a grain of rice, located on the posterior surface (back side) of the thyroid gland. The parathyroid glands are named for their proximity to the thyroid but serve a completely different role than the thyroid gland. They are quite easily recognizable from the thyroid as they have densely packed cells, in contrast with the follicle structure of the thyroid. However, at surgery, they are harder to differentiate from the thyroid or fat.