under the paracortical zone there are cords of lymphatic tissue (medullary cords) and the spaces between them (medullary sinuses)

are "customs barriers" for all "regional" antigens

сortical substance contains lymphoid follicles (B-cell zone or B-cell follicles)

parenchyma is composed of T- and B-cell zones, and medullary cords

T-lymphocytes  are located in the paracortical (T-cell) zone