Originally: a region of the brain of reptiles and birds thought to represent an intermediate stage in the phylogenetic development of the corpus striatum of mammals. In later use specifically: a heterogeneous region of the avian brain having sensory-motor and limbic connections, and corresponding in part to the mammalian amygdala.
The preferred name for this region of the avian brain is now arcopallium.
Early 20th century. From archi- + striatum, after German Archistriatum.