The corpus luteum is indeed found in the ovary (option 2). It is a mass of cells that forms in an ovary and is responsible for the production of the hormone progesterone during early pregnancy. It plays a critical role in the female reproductive system.

Option 1, the brain, is incorrect as the corpus luteum is not found there. The brain is more related to the nervous system rather than the reproductive system.

Option 3, the pancreas, is also incorrect. The pancreas is an organ of the digestive system that produces enzymes and hormones, but it has no direct involvement in the production or housing of the corpus luteum.

Option 4, the spleen, is another incorrect choice. The spleen helps filter blood, fight bacterial infections, and it also recycles old red blood cells, but it has no connection or correlation with the corpus luteum.

Therefore, the correct and only suitable option for the location of the corpus luteum is the ovary.