the thymus is located in the , anterior to the aortic arch. the is very large in a child and will atrophy in advanced age. the is the largest of the lymphatic organs. a of connective tissue surrounds the spleen. the tiny islands (nodules) of tissue within the spleen that contain many lymphocytes constitute the pulp. the pulp of the spleen contains large numbers of red blood cells, lymphocytes, and macrophages. within the spleen engulf and destroy foreign particles and cellular debris. the lymphoid organs in the pharynx (throat) that are possible infection sites are collectively called the .