(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 posterior median sulcus is the posterior end of the posterior median septum of neuroglia of the spinal cord. The septum varies in depth from 4 to 6 mm, but diminishes considerably in the lower part of the spinal cord.he posterior median sulcus is the posterior end of the posterior median septum of neuroglia of the spinal cord. The septum varies in depth from 4 to 6 mm, but diminishes considerably in the lower part of the spinal cord.