192 Report on the Pathological Anatomy of Pleuro-pneumonia. 
Occasionally, however, the lymphatics may be affected to an 
enormous extent ; in one case the disease reached to the trachea, 
and caused partial occlusion of it, by filling the numerous 
lymph vessels which occupy the posterior part behind the 
trachealis muscle (Fig. 3). In these cases the lymphatic glands 
of the root of the lung are much enlarged, but as a general rule 
do not become caseous. 
Fig. 3. — Surface of Transverse Section of Trachea in which the 
Lymphatics are intensely engorged. 
M. Mucous membrane. C. Cartilage. T. Trachealis muscle. L. Comiective tissue and engorged 
lymph-channels. 
In speaking of the normal structure of the lung of the ox, I 
called attention to the very intimate relation between the 
bronchial tubes and the blood-vessels. They pass along the 
same grooves in the lung parenchyma, are surrounded by the 
same sheath of thin connective tissue, and their lymphatics 
communicate freely with those of each broncho-vascular system, 
forming one large set of absorbents, which carries all the lymph 
of the territory supplied by the bronchial tube and its accom- 
panying vessels. It is not at all surprising, then, that as the 
morbid changes just described are going on in the peribronchial 
tissue, the sheath of the blood-vessels participates in the diseased 
action. The exudation encloses the blood-vessels at the same 
time that it thickens the tissue around the bronchus. So that 
instead of the three vessels lying in a loose bed of soft tissue, 
they are encased in a frame, which, enclosing them all, soon 
becomes so tough and rigid, that they remain patent cylinders, 
