THE LYMPHATIC SYSTEM. 97 



f Capsule. 

 Adenoid tissue. 



Tonsils Mucous g-lands. 



[ Blood and lymph corpuscles. 



LYMPHATIC TISSUE. 



Lymphatic tissue is composed chiefly of two structures: (1) A 

 connective tissue reticulum. This is commonly known as adenoid, 

 or retiform tissue. (2) The lymphoid cells, which are held in the 

 meshes of the reticulum. These escape into the lymphatic vessels 

 and are there known as the lymph corpuscles. They eventually 

 become the leucocytes of the blood. 



LYMPHATIC VESSELS. 



The lymphatic vessels are irregular in outline, due to folds in 

 the endothelium, which serve as imperfect valves. The wall of each 

 vepsel exhibits three coats. The inner coat consists of endothelium, 

 the middle of smooth muscle, and the outer of connective tissue. 



LYMPHATIC FOLLICLES. 



These have been classified as simple .nodules and compound lym- 

 phatic nodes. The simple nodule consists of a capsule and adenoid 

 tissue with enclosed lymphoid cells. The compound lymphatic 

 node exhibits capsule, reticulum of connective tissue, cortex, and 

 medulla. The capsule is the sheath of connective tissue which cov- 

 ers the node and from which septa, or trabeculas, extend into its 

 substance. The cortex is the outer zone of the body, and consists 

 of the cortical follicles and the germinal center. The cortical folli- 

 cles are the laboratories in which are manufactured the leucocytes. 

 The germinal center is a light spot within the follicle, characterized 

 by the presence of kinetic figures. The medulla is the central por- 

 tion of the gland. It contains the medullary bands, which are sim- 

 ply extensions of the trabeculae into its substance. TJhis mesh- work 

 formed by the subdivision of the trabeculae constitutes the reticulum. 

 The Jiilum is an infolding of the capsule upon a blood-vessel or 

 lymph channel at its point of entrance into the gland. Sinuses are 

 the open spaces between the adenoid tissue and trabeculae. 



