(1) One quarter of a circle. (2) anatomy roughly circular areas are divided for descriptive purposes into quadrants. The abdomen is divided into right upper and lower and left upper and lower quadrants by a horizontal and a vertical line intersecting at the umbilicus. The breast is divided into quadrants by vertical and horizontal lines that intersect in the center of the nipple. Quadrants of the ocular fundus (superior and inferior nasal, superior and inferior temporal) are demarcated by a horizontal and a vertical line intersecting at the optic disc. The tympanic membrane is divided into anterosuperior, anteroinferior, posterosuperior, and posteroinferior quadrants by a line drawn across the diameter of the drum in the axis of the handle of the malleus and another intersecting the first at right angles at the umbo. [L. quadrans, a quarter]