LYMPHATIC GLANDS 



251 



vessels enter and the efferent vessels emerge, and are covered, except 

 at the hilum, with a delicate membrane composed of inelastic fibres, 

 a few elastic fibres and non-striated muscular fibres. Their exterior is 

 somewhat tuberculated, from the projections of the follicles just beneath 

 the investing membrane. The interior of the glands is soft and pulpy. 

 It presents a coarsely-granular cortical substance, of a reddish white 

 or gray color, which is ^ to | of an inch (4 to 6 millimeters) in thick- 

 ness in the largest glands. 

 The medullary portion, which 

 comes to the surface at the 

 hilum, is lighter colored and 

 is coarser than the cortical 

 substance. Throughout the 

 gland are found delicate 

 fasciculi of fibrous tissue con- 

 nected with the investing 

 membrane, which serve as a 

 fibrous skeleton for the gland 

 and divide its substance into 

 alveoli. The structure is far 

 more delicate in the cortical 

 than in the medullary portion. 

 Within the alveoli are irreg- 

 ularly-oval closed follicles 

 (lymph-nodules), about 3^0 ^ 

 an inch (100 At) in diameter, 

 filled with liquid and with 

 cells like those contained in 

 the solitary glands of the in- 

 testines and the patches Of Fi S- (*>- Lymphatics and lymphatic glands (Mascagni). 

 p^v^r Trip rp11 cnm^ * u PP er extremity of the thoracic duct, passing behind 



II1C " the internal jugular vein ; 2, opening of the thoracic duct 



times Called lymph-Cells into the internal jugular and left subclavian veins. The 



., -, . , . , lymphatic glands are seen in the course of the vessels. 



are situated at the periphery 



of the nodules ; and in the centre is a relatively clear zone called the 

 germ-centre. The nodules do not occupy the medullary portion of the 

 glands, which is composed chiefly of a network of lymphatic capillaries 

 mixed with rather coarse bands of fibrous tissue. The follicular struc- 

 tures in the lymphatic glands resemble the closed follicles in the mucous 

 membrane of the intestinal canal and the Malpighian bodies of the 

 spleen (see Plate VIII). 



In the substance of the lymphatic glands are great numbers of lymph- 

 spaces or canals, which probably are lined with endothelium ; and these 



