Which of the following organs is NOT found in the abdominal cavity?

The brain is the correct answer because it is located in the cranial cavity, which is part of the skull, and not in the abdominal cavity. The abdominal cavity primarily contains the digestive organs, such as the stomach, liver, and spleen, which play crucial roles in digestion and metabolic functions. The separation of these cavities is significant in anatomy as each area supports different organ systems with distinct functions. Therefore, the brain, being a part of the central nervous system, is not associated with the abdominal cavity where the listed abdominal organs are located.