substantia gelatinosa

noun

substantia gel·​a·​ti·​no·​sa -ˌjel-ət-ᵊn-ˈō-sə 

: a mass of gelatinous gray matter that lies on the dorsal surface of the dorsal column and extends the entire length of the spinal cord into the medulla oblongata and that functions in the transmission of painful sensory information