162 



PRACTICAL MICROSCOPY. 



LYMPH CHANNELS. 



The larger and more regularly formed channels for lymph circu- 

 lation, such as the mesenteric and thoracic ducts, do not differ, 

 materially, in structure, from correspondingly sized veins. The 

 irregular clefts in the interstices of fibrous tissues, serving as 

 the primitive lymph-containing channels, have been already, 

 and repeatedly, noticed. Fig. 109, although purely diagrammatic, 

 will serve to show the relation of this system to the blood-vessels. A 

 perivascular lymphatic channel is a sort of tubular investment of the 



MEDIA 

 ADVENTITIA 

 ERIVASCULAR 



FIG. 109. DIAGRAM. ARTERY IN TRANSVERSE SECTION, SHOWING THE PERIVASCULAR 



LYMPH-SPACE. 



blood-vessel, lined with flattened endothelia sending prolongations 

 inward; these prolongations branch, and are finally in communication 

 with a layer of cells covering the adventitia. In this manner, in 

 close apposition to parts of the vascular system, a system of channels 

 is provided, within which the lymph may sloivly percolate. 



The largest lymphatic channels in the human body are the cavities 

 of the peritoneum and pleurae. They are in connection one with the 

 other, and with the lymphatic system generally; and these channels 

 of communication between the great abdominal and thoracic lym- 

 phatic cavities present, perhaps, as the most convenient and typical 

 for demonstration. 



