THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 39 



the form of cords which originate in the fusion of several peri-lym- 

 phangial nodules. 



To summarise the preceding statements, we may divide the 

 lymphatic nodules into peri- and endo-lymphangial : the former consti- 

 tute isolated nodules or patches, and, by fusion, cords ; the latter form 

 patches and nodules, and, by continuous outgrowth, cords. From what 

 I have seen in the omentum and pleura mediastini of guinea-pigs, 

 dogs, cats and monkeys, I am inclined to think that along one 

 lymphatic vessel several endo-lymphangial nodules may originate, 

 isolated, which afterwards become fused together, so as to form a 

 cord. 



It seems to me that the development of the peri-lymphangial 

 nodules follows more the arterial vessels, whereas that of the endo- 

 lymphangial nodules the venous vessels. My researches have, how- 

 ever, not been carried out so far as to enable me to state this with 

 certainty. 



We come now to the lymphatic system of the omentum and pleura 

 mediastini of the animals just mentioned. We are able to treat this 

 part more briefly, since we have stated the essential points in detail 

 in the preceding, where, in the omentum of the rabbit namely, the 

 proof of the facts brought forward is considerably easier to adduce 

 than for the first-named animals. The lymphatics in the normal 

 state are here much more difficult to demonstrate than in the rabbit. 

 It is desirable to select for studying preparations mounted quite 

 fresh in serum, and subjected to the least possible tearing. One may 

 be prepared for ill-success in many cases of staining the omentum 

 with silver. It is very difficult to pencil accurately the extremely 

 delicate fenestrated portion of the omentum. The best preparations 

 are obtained from the guinea-pig, from that part of the omentum in 

 which the pancreas lies enveloped. It is less difficult to pencil the 

 omentum of the cat, the rabbit, or the ape, because here the omentum 

 lies on the small intestine like an apron. It is equally difficult to 

 obtain a successful preparation of the pleura mediastini of the guinea- 

 pig as well as of the cat, there being in the latter case an unusual 

 number of trabeculae, running in all directions free on the surface, 

 bearing the lymphatic nodules, which trabeoulge interfere to a great 



