OF THE LYMPHATIC VESSELS. 307 



Jess voluminous than the deeply seated ones. The size of 

 these vessels is much less than that of the veins. Those of 

 the inferior extremities are larger than those of the superior 

 members, those of the head are very small. As to their ag- 

 gregate capacity, it has not been accurately determined; it 

 appears generally to be nearly double that of the arteries, and 

 to equal that of the veins in the superficial plane at least. 



464. The origin of the lymphatic vessels is invisible and un- 

 known. Physiological considerations and anatomical experi- 

 ments have caused authors first to admit and then to reject their 

 direct and immediate continuation with the arteries. We have 

 also seen that the origin admitted to take place by open orifices 

 at the surface of the two tegumentary and serous membranes, 

 in the areolae of the cellular tissue, and in the substance of the 

 organs, which has been deduced from considerations and ex- 

 periments of the same kind, is not better founded. It is well 

 to know how to doubt. 



465. As soon as they can be perceived, the radicles of the 

 lymphatic vessels are seen to unite together, to separate, and 

 unite anew, so as to form net-works which constitute in a 

 great measure the serous, tegumentary and other membranes. 



These vessels become generally larger and more numerous 

 as they are farther removed from their origin. In their course 

 they continue to divide into branches, which reunite with 

 other neighbouring branches, or even with each other, so as 

 to form parts entirely surrounded by liquid. These divisions 

 and these numerous anastomoses form plexuses in many 

 places. 



When they are full and a little distended they appear rather 

 moniliform than cylindrical. This appearance of a rosary is 

 owing to the great number of valves with which they are pro- 

 vided, and to the dilatation which they present above them. 

 They also frequently present ovoid dilatations. We observe 

 in them many variations in their course: those of one side al- 

 ways differ more or less from those of the other. 



All the lymphatic vessels, after a longer or shorter course, 

 ramify in the same manner as the arteries, and seem to ter- 

 minate in lymphatic glands, beyond which they reappear again 



