CHAPTER XII 

 LYMPHATIC ORGANS 



Lymphatic Tissue ' 



)0-CALLED lymphatic tissue consists of reticular connective tissue 

 and a special type of cells, lymphoid cells, which fill in the meshes of 

 the reticulum. Lymphoid cells are small spheroidal cells, each hav- 

 ing a single nucleus which almost completely fills the cell. Lym- 

 phatic tissue may be difi'use or circumscribed. In diffuse lymphatic 

 tissue the cells are not closely packed and there is no distinct de- 

 marcation between the lymphatic and the surrounding tissues. An 

 example of difi'use lymphatic tissue is seen in the stroma of the 

 mucous membrane of the gastro-intestinal canal. In circumscribed 

 lymphatic tissue the cells are very closely packed, often completely 

 obscuring the reticulum. There is also a quite distinct demarca- 

 tion between the lymphatic and the surrounding tissues. Such a 

 circumscribed mass of lymphatic tissue is known as a lymph nodule. 



The Lymph Nodes 



Lymph nodes are small bodies, usually oval^or bean-shaped, which 

 are distributed along the course of the lymph vessels. In some 

 regions they are arranged in series forming "chains" of lymph 

 node^as, e.g., the axillary and inguinal. 



'liEach lymph node is surrounded by a capsule of connective tissue 

 which sends trabeculaor sepja into the organ. The capsule and septa 

 constitute the connective-tissue^[ramewqrk_ of the node, and serve as a 

 support for the lymphatic tissue (Fig. 99). 



The capsule is composed of fibrous connective tissue. Toward 

 the surface of the capsule the fibres are loosely arranged and there 

 are comparatively few elastic fibres. This outer layer of the capsule 



^ In the preceding editions " lymphatic tissue" was placed according to name rather 

 than structure among the tissues. As it consists of a connective tissue framework sup- 

 porting a special type of cell which has a specific function, it is more properly classi- 

 fied as an organ. On account of the peculiar structure and wide distribution of the 

 "tissue" and on account of convenience and long usage, the term " lymphatic tissue" 

 is still retained. 



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