(Botany) an association of a fungus and a plant in which the fungus lives within or on the outside of the plant's roots forming a symbiotic or parasitic relationship. See ectotrophic mycorrhiza, endotrophic mycorrhiza. [C19: from myco- + Greek rhiza root]
Medical Definition of POSTERIOR MEDIAN SULCUS. : a shallow groove along the midline of the posterior part of the spinal cord that separates the two posterior funiculi and is the external boundary of the posterior median septum. a shallow groove along the midline of the posterior part of the spinal cord that separates the two posterior funiculi and is the external boundary of the posterior median septum.
a groove or furrow; used in anatomic nomenclature to designate a linear depression, especially one of the cerebral sulci. basilar sulcus a groove in the midline of the anterior surface of the pons, lodging the basilar artery. calcarine sulcus a sulcus of the medial surface of the occipital lobe, separating the cuneus from the lingual gyrus.