32 ANATOMY OF THE LYMPHATIC SYSTEM. 



In the portion of omentum covering the anterior wall of the 

 stomach the conditions are somewhat different. There it will be seen 

 that the lymphatics run only in company with the blood-vessels ; large 

 blood vessels, again, are rare in that part, the vessels of common 

 occurrence being the smaller arteries and veins, which, however, run 

 quite isolated, often for a considerable distance. The arrangement 

 of the lymphatics is as follows. Either a single lymphatic vessel 

 is accompanied on one side frequently by a vein and sometimes also 

 by an artery : the lymphatic keeps close to the blood vessel, possesses 

 at certain points sacciform dilatations, and receives also sometimes a 

 branch laterally. These are vessels that have mostly a sinuous 

 endotheliiun. Or, secondly, it may happen that a blood-vessel is 

 accompanied on both sides by a lymphatic : these are disposed exactly 

 as in the former case, and communicate by cross branches. } 



Finally, it occurs not unfrequently that the blood vessel runs 

 within a lymphatic that the blood-vessel is invaginated. There 

 cannot be the slightest doubt that such invaginations occur. They 

 are of various kinds. One case, for example, which is quite easy to 

 make out, is that of a vein invaginated for a considerable part of its 

 course, while, at the same time all its branches, so long as they are 

 not capillaries, are also invaginated. The chief lymphatic, containing 

 the venous trunk, leaves the latter, after a long course, at a point where 

 this vein opens into a larger trunk, and then unites with the 

 lymphatic that accompanies this principal venous trunk. It may 

 also happen, secondly, that the lymphatic leaves the blood-vessel long 

 before the latter opens into a large trunk : in this case the vein and 

 lymphatic run side by side to the latter point. Finally, there is a 

 third case, which, however, in the omentum is much rarer, viz. where 

 the lymphatic accompanying a blood-vessel (and invaginating it) 

 suddenly acquires an extensive dilatation, through which the blood- 

 vessel penetrates, breaking off at an angle, while the lymphatic can be 

 traced a long way beyond the dilatation. 



All these descriptions are drawn from preparations that have been 

 pencilled and silvered. I have in my possession preparations of 

 rabbit's omentum where such perivascular lymphatics present them- 

 selves as large tubes, the walls of them showing the sinuous endothe- 



