THE CIRCULATORY SYSTEM. 121 



pression at one point, called the " hilns." It is invested by a fibrous 

 capsule, which is of areolar character externally, where it connects 

 the node with surrounding structures, but is denser, and frequently 

 reinforced by a few smooth muscular fibres internally. Extensions 

 from this capsule penetrate into the substance of the node, forming 

 " trabecular," which support the structures making up the body of 

 the node. 



The lymphadenoid tissue occurs in two forms : first, as spherical 

 masses, " follicles," lying toward the periphery of the node, except at 

 the hilus, and constituting the "cortex" (Fig. 105); second, in the 



Fig. 105. 



— i 



'i 'i ■ . 



-»-«:_ ' -lb 







k> 





• 





Single lymph-follicle from a mesenteric node of the ox. (Flemming.) lb, wide-meshed 

 lymphatic sinus at periphery of the follicle. Between this and the peripheral zone of 

 the follicle z, and within the follicle, the reticulum of the sinus and that supporting the 

 cells and vessels of the follicle are not represented. The cells are merely indicated by 

 their nuclei, the cytoplasm being r omitted. z, peripheral zone of the follicle, marked by 

 a close aggregation of small lymphoid cells; p, more scattered cells outside of the 

 peripheral zone and at the edge of the lymph-sinus. Within the zone z is the germinal 

 centre of the follicle, in which numerous karyokinetic figures are'present, demonstrating 

 the active proliferation of the cells in that region. Two such figures are also represented 

 within the lymph-sinus at the upper left corner. 6, bloodvessels. 



form of anastomosing strands, which makes a coarse meshwork of 

 lymphadenoid tissue in the medullary portion of the node (Fig. 106). 

 The trabecular springing from the capsule penetrate the substance 

 of the node between the follicles in the cortex, and then form a net- 

 work of fibrous tissue lying in the meshes of the medullary lymph- 

 adenoid tissue, after which they become continuous with the mass 



