174 THE ORGANS 



The regular arrangement of trabecular, and lymph nodules with 

 sinuses betv;een, which is characteristic of the cortex, makes this 

 part of the organ easily understood. To appreciate the structure of 

 the medulla it must be borne in mind that all of these cortical struc- 

 tures extend down into the medulla, the trabeculse as anastomosing 

 networks of connective tissue, the lymph nodules as cord-like struc- 

 tures which divide and anastomose, the sinuses as more or less 

 clear channels which always separate the connective tissue from the 

 lymph cords. These parts — trabecula, sinus, lymph cord— all anas- 

 tomosing freely and most irregularly in the medulla, always main- 

 tain the same relation to one another as in the cortex, namely, 

 that sinus is always interposed between lymph tissue and trabecula. 



The reticular connective tissue (page 98), which forms a part of 

 the lymphatic tissue proper, is continuous with the fibrous connec- 

 tive-tissue framework of the organ in such a manner that it is im- 

 possible to determine any demarcation between the two tissues. In 

 the lymph nodules, and wherever the lymphoid cells are densely 

 packed, the underlying reticular network is almost completely ob- 

 scured. ''a Crossing the sinuses, especially those of the medulla, and 

 in specimens in which the cells have been largely washed out or 

 removed by maceration, the reticular structure is well shown. 



^ The lymphoid tissue proper, as represented by the lymph nodules 

 and anastomosing lymph cords, is thus, as it were, suspended in the 

 meshes of a reticulum which is swung from the capsule and trabec- 

 ulas. As both nodules and cords are everywhere separated from cap- 

 sule and trabecular by the sinuses, and as these latter serve for the 

 passage of lymph through the node, it is seen that the lymphatic tis- 

 sue of the node is broken up in such a manner as to be bathed on 

 all sides by the circulating lymph.! 1 



In addition to the definitely formed lymph nodes and the well- 

 defined collections of lymph nodules, such as those of the tonsil or 

 of Peyer's patches, small nodules or groups of lymphoid cells have a 

 wide distribution throughout the various organs. While many of 

 these collections of lymphatic tissue are inconspicuous, still the ag- 

 gregate of lymph tissue thus distributed is by no means inconsider- 

 able. The most important will be described in connection with the 

 organs in which they occur. 



Blood-vessels.^ — Those which enter the hilum carry the main 

 blood supply to the organ. Most of the arteries pass directly into 

 the lymphatic tissue, where they break up into dense capillary net- 



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