THE LYMPHATIC SYSTEM. 



937 



^^;v. 



the birthplaces of new lymphocytes. Although the limits of the lymph-nodules are 



commonly imperfectly defined by a condensation of the surrounding connective 



tissue, a distinct capsule is usually wanting. 



Definite lymph-channels are found neither Fig. 78S. 



upon the surface nor within the simple 



nodules ; the latter are provided, however, 



with a generous net-work of capillary 



blood-vessels (Fig. 792). 



Intermediate in their complexity of 

 arrangement, between the simple nodules 

 on the one hand and the typical lymph- 

 nodes on the other, stand such structures 

 Fever's patches and the faucial and 



as 



pharyngeal tonsils, in which groups of 

 simple nodules are blended into a single 

 organ, the component follicles only partly 

 retaining their individuality. 



The lymph-nodes interposed along 

 the lymphatic vessels, usually embedded 

 within fatty tissue, represent still higher 

 differentiation as distinct organs. In form 

 and size they vary from minute bodies 

 resembling millet-seeds to flattened oval or 

 bean-shaped organs, that may measure almost an inch in their longest diameter. 

 They are invested by a distinct fibrous capsule, in which elastic fibres constantly and 

 unstriped muscle occasionally are present. PVom the deeper surface of this envelope 

 numerous radially directed trabeculae penetrate the outer zone, or cortex, which is 

 thus subdivided into a series of pyramidal compartments. On reaching the inner 

 limits of the cortical zone, the trabeculae are less regularly disposed and more freely 

 united, thereby breaking up the deeper parts, or medulla, of the node into uncertain 

 cylindrical compartments. The spaces thus imperfectly defined by the trabeculae are 



Portion ot lymph-iiodule, showing details 

 of germ-centre. X 350. 



Germ centre 

 Lymph sniu'> 



Fat 



Fig. 789. 



Lymph-sinus 



Capsule 

 frabecula 



Cortical follicles 



Lymph-sinus 



Hilum 



\ asa efTerentia 



Medullar^ Lords 



Section of small lymph-node through hilum. X 25. 



incompletely filled by masses of compact lymphoid tissue, the general form and 

 arrangement of which correspond to the compartments in which they lie. The masses 

 contained within the peripheral spaces are spherical or pyriform and constitute 



