(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 ventral ramus of thoracic nerve 12 is known as the subcostal nerve. It enters the abdomen posterior to the lateral arcuate ligament, crosses posterior to the kidney, penetrates the muscles of the abdominal wall, enters the rectus sheath, and becomes cutaneous (see fig. 25-12).