SECTION V 
DISEASES OF THE LYMPHATIC TISSUES 
INCLUDING SPLEEN 
Since we have followed diseases of the blood from the 
simple anemias to a place where mononucleosis in the 
circulatory system and in the fixed tissues is the promi- 
nent feature, another step reaches the area whence most 
of these cells emanate — the lymphatic system. The 
anatomical and physiological position of the lymphatic 
circulatory apparatus is closely analogous in the classes 
under discussion, and it stands in an anatomico-clinical 
sense, closer to the hematopoietic system than to any 
other structures, throughout the whole animal creation. 
This anatomical division of the circulation is closely com- 
parable, for pathological purposes, in the mammals 
whereas in the birds one finds noteworthy variations. 
In the class Aves IjTuphatic radicals are extremely 
numerous, the plexuses in the extremities and thorax 
perhaps being complemental for the rather scantily sup- 
plied blood vessels. About the fibulo-tibial and femoral 
muscles the tiny lymph vessels form an extraordinarily 
dense and intricate lacework, a repUca of which may be 
found in muscles of the upper limb, while in the pelvis 
and thorax a rich plexus is distributed around both kinds 
of blood vessels and also lies within the walls of air sacs. 
The air sac walls in the chest display lymphatic lines 
very well in birds that have been for many years exposed 
to railway dust, the natural pearl gray glistening mem- 
brane looking as if black pepper had been evenly dusted 
over it. The honph glands or compound nodes so easily 
discovered in mammals are practically absent in birds. 
Along the large thoracic vessels and in the pelvis of some 
anserine and struthious varieties, small illy defined 
masses of lymphatic tissue may be discovered by careful 
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