(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.
The coccygeal nerves are attached to it. The cord presents a posterior median sulcus and an anterior median fissure, lateral to which the dorsal and ventral root filaments are attached (figs. 41-2 and 41-3). The segment of spinal cord to which a given pair of dorsal and ventral roots is attached is a myelomere (fig. 41-2).