The third normal plane is the cingular (waist) plane: this is defined by the sagittal and transverse axes.
cingulum cin·gu·lum (sĭng'gyə-ləm)
n. pl. cin·gu·la (-lə)
A structure that has the form of a belt or girdle.
A well-marked fiber bundle passing longitudinally in the white matter of the cingulate gyrus, composed largely of fibers from the anterior thalamic nucleus to the cingulate and parahippocampal gyri.