(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.
n. The longitudinal groove marking the posterior midline of the medulla oblongata and continuous below with the posterior median sulcus of the spinal cord. Also called posterior median fissure.asilar 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.