LYMPH- CHANNELS 



107 



The direction of the lymph- current is determined by valves 

 which resemble somewhat those of the veins. 



Cavities lined with so-called serous membranes may be consid- 

 ered as expanded lymph -channels. 



LYMPH- CHANNELS 



The larger and more regularly formed channels for lymph-cir- 

 culation, such as the mesenteric arid 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, will be repeatedly noticed 

 in studying the various organs. Fig. 75, although purely dia- 



INTIMA 



MEDIA 



ADVENTITIA 

 rPEfWASCULAR 

 (. SPACE 





FIG. 75. DIAGRAM. ARTERY IN TRANSVERSE SECTION, SHOWING THE 

 PERI VASCULAR LYMPH-SPACE. 



grammatic, will serve to show the relation of this system to the 

 blood-vessels. A peri vascular lymphatic channel is a sort of 

 tubular investment of the blood-vessel, lined with flattened endo- 

 thelium 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 $f the 

 vascular system, a system of channels is provided, within which 

 the lymph may slowly percolate. They are usually found about 

 the arteries of the central nervous system. 



The largest lymph -spaces in the human bodj r are the cavities 

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

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

 channels of communication between the great abdominal and 



