The specific brain structure that contains the intermediate mass is the thalamus. The intermediate mass, also known as the massa intermedia, is a small, flattened band of gray matter that connects the two thalami across the third ventricle of the brain.
The thalamus plays a crucial role in relaying sensory and motor signals to the cerebral cortex. The presence of the intermediate mass is significant as it allows for communication between both sides of the thalamus, facilitating the integration of sensory information. Although not everyone has an intermediate mass—some people may have a complete separation of the two thalami—it is still an interesting and important feature of brain anatomy.