(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.
Below the arcuate line, the aponeuroses remain intact anteriorly, but only the weak transversalis fascia and peritoneum separate the muscle mass from the abdominal viscera posteriorly. The inferior retrorectus space communicates with the prevesicular space of Retzius. This communication creates a natural dissection plane between the posterior rectus sheath and the bladder. Anatomy of the rectus sheath.