LYMPH GLANDS. 



157 



native centers. These are sometimes called secondary nodules. The 

 medullary portion includes cord-like prolongations of the nodules, called 

 medullary cords. The secondary nodules often are incompletely separated 

 from one another and the cords join to form a network. Both the nodules 

 and the cords are enveloped by the lymph sinuses, and the trabeculae if 

 present are in the midst of the sinuses (Figs. 177 and 178). The nodules 

 and cords are both composed of lymphocytes in a close-meshed reticular 

 tissue. 



The blood vessels of the lymph gland in part enter from various 

 points in the capsule and run in the trabeculae, but the chief vessels enter 

 at the hilus. The artery divides into several branches which remain in 



FIG. 177. FIG. 178. 



FROM VERTICAL SECTIONS THROUGH THE MEDULLA OF A LYMPH GLAND OF AN Ox. 



Fig. 1 7 j, X 50, shows the medullary cords and trabeculae cut lengthwise in its upper part, and cut across 

 in its lower part. Both the cords and the trabeculae form continuous networks. Fig. 178, X 240, 

 shows the fine reticular tissue of the lymph sinus, containing a few leucocytes. 



the trabeculae for only a short distance, and then cross the lymph sinuses 

 to the medullary cords. They extend through the axes of the cords into 

 the nodules, giving off small branches which form capillary networks and 

 unite in veins found at the periphery of the nodules and cords. The veins 

 soon cross the sinuses and enter the trabeculae in which they travel toward 

 the hilus. A central artery, surrounded by lymphoid tissue together with 

 peripheral veins, is found not only in lymph glands but also in the spleen. 

 The lymphatic vessels penetrate the capsule at several points and become 

 involved in the lymph sinuses. Through these, partly in endothelial tubes, 

 and partly in tissue spaces, the lymph flows toward the hilus which it 



