<P> Lymph enters the convex side of the lymph node through multiple afferent lymphatic vessels, and flows through spaces called sinuses . A lymph sinus which includes the subcapsular sinus, is a channel within the node, lined by endothelial cells along with fibroblastic reticular cells and this allows for the smooth flow of lymph through them. The endothelium of the subcapsular sinus is continuous with that of the afferent lymph vessel and is also with that of the similar sinuses flanking the trabeculae and within the cortex . All of these sinuses drain the filtered lymphatic fluid into the medullary sinuses, from where the lymph flows into the efferent lymph vessels to exit the node at the hilum on the concave side . These vessels are smaller and don't allow the passage of the macrophages so that they remain contained to function within the lymph node . In the course of the lymph, lymphocytes may be activated as part of the adaptive immune response . </P> <P> The lymph node capsule is composed of dense irregular connective tissue with some plain collagenous fibers, and from its internal surface are given off a number of membranous processes or trabeculae . They pass inward, radiating toward the center of the node, for about one - third or one - fourth of the space between the circumference and the center of the node . In some animals they are sufficiently well - marked to divide the peripheral or cortical portion of the node into a number of compartments (nodules), but in humans this arrangement is not obvious . The larger trabeculae springing from the capsule break up into finer bands, and these interlace to form a mesh - work in the central or medullary portion of the node . In these trabecular spaces formed by the interlacing trabeculae is contained the proper lymph node substance or lymphoid tissue . The node pulp does not, however, completely fill the spaces, but leaves, between its outer margin and the enclosing trabeculae, a channel or space of uniform width throughout . This is termed the subcapsular sinus (lymph path or lymph sinus). Running across it are a number of finer trabeculae of reticular connective tissue, the fibers of which are, for the most part, covered by ramifying cells . </P> <P> The subcapsular sinus (lymph path, lymph sinus, marginal sinus) is the space between the capsule and the cortex which allows the free movement of lymphatic fluid and so contains few lymphocytes . It is continuous with the similar lymph sinuses that flank the trabeculae . </P> <P> The lymph node contains lymphoid tissue, i.e., a meshwork or fibers called reticulum with white blood cells enmeshed in it . The regions where there are few cells within the meshwork are known as lymph sinus . It is lined by reticular cells, fibroblasts and fixed macrophages . </P>

Lymph node clusters are found in which region