Diencephalon is made of three main parts:
1. Thalamus which is a relay station for sensory input
2. Epithalamus which have the function in producing spinal fluid and in the secretion of melatonin by the pineal gland
3. Hypothalamus which links the endocrine with nervous system.
There is also another structure inside diencephalon sometimes called the fourth structure. It is subthalamus which regulates skeletal muscle movements.