Which of the following is a major endocrine gland?

The pituitary gland is a major endocrine gland because it plays a crucial role in regulating various hormonal functions in the body. Often referred to as the "master gland," the pituitary gland is located at the base of the brain and produces hormones that control other glands in the endocrine system, such as the thyroid, adrenal glands, and gonads. It releases hormones like growth hormone, prolactin, and adrenocorticotropic hormone, which influence growth, metabolism, and stress responses, among other physiological processes.

In contrast, the other options listed—corpus callosum, cerebral cortex, and thalamus—are all part of the central nervous system and not classified as endocrine glands. The corpus callosum is a bundle of nerve fibers connecting the two cerebral hemispheres, the cerebral cortex is involved in higher brain functions such as thought and action, and the thalamus acts as a relay station for sensory information. None of these structures produce hormones or are involved in the endocrine system's regulatory functions.