LYMPH GLANDS 2OQ 



same tissues. They are completely surrounded by the lymph sinuses as 

 shown in Fig. 197. The flat cells over their surfaces may be regarded as 

 endothelial cells. 



The blood vessels of a lymph gland enter chiefly at the hilus, but in 

 the larger glands some of them come in from the periphery and run in 

 the trabeculae; others however pass out through the trabeculse into the 

 capsule. The principal artery enters at the hilus and divides at once 

 into several branches, which travel in the trabeculae for a short distance, 

 and then pass over into the medullary cords. They extend through the 

 axes of the cords into the nodules, giving off small branches which form 

 a venous network at the periphery of these structures. The veins which 

 drain this network soon cross the sinuses and enter the trabeculae, in 

 which they travel toward the hilus alongside the arteries (Calvert, Anat. 

 Anz., 1897, vol. 13, pp. 174-180). A central artery surrounded by lymph- 

 oid tissue and drained by peripheral veins is found not only in lymph 

 glands, but also in the spleen. 



Nerves to the lymph glands are not abundant. They consist of medul- 

 lated and non-medullated fibers, which form plexuses about the blood 

 vessels, and supply the muscle cells in the capsule and trabeculae. They 

 have not been found in the nodules and cords. 



The function of the lymph glands is not only to produce lymphocytes 

 which enter the lymphatic vessels and are conveyed through the thoracic 

 duct into the blood, but also to "filter the lymph." If certain poisonous 

 substances, inert particles, or bacteria are brought to the gland in the 

 lymph, they may be removed by the phagocytic endothelial or reticular 

 tissue cells. The gland at the same time may become enlarged by con- 

 gestion, and by multiplication of its cells. 



H^EMOLYMPH GLANDS. 



Haemolymph glands resemble small lymph glands, ranging in size 

 from a "pin-head to an almond." They occur especially in the retro- 

 peritoneal tissue near the origin of the superior mesenteric and renal ar- 

 teries, but are found elsewhere, and it has been said that their distribution 

 coincides with that of ordinary lymph glands. They are darker than the 

 lymph glands, and on section yield blood in place of lymph. No lymph- 

 atic vessels are associated with them, when typically developed, and in- 

 stead of a lymph sinus they possess a similar structure filled with blood, 

 the blood sinus. The lymphoid tissue with its blood supply, together with 

 the capsule and trabeculae, are like the corresponding structures in lymph 

 glands. The capillary blood vessels, however, are readily permeable, 

 so that their contents, both plasma, and corpuscles, escape into the blood 

 sinus. The haemolymph gland is therefore a "blood filter." Many 

 14 



