[TA] a shallow depression, blue in the fresh brain, lying laterally in the most rostral portion of the rhomboidal fossa near the cerebral aqueduct; it lies near the lateral wall of the fourth ventricle and consists of about 20,000 melanin-pigmented neuronal cell bodies the norepinephrine-containing axons of which have a remarkably wide distribution in the cerebral cortex, dorsal thalamus, amygdaloid complex with the hippocampus, mesencephalic tegmentum, cerebellar nuclei and cortex, various nuclei in the pons and medulla, and the gray matter of the spinal cord.