378 



MANUAL OF HISTOLOGY. 



Fig 380. A lymphatic canal 

 from the large intestine of 

 the Guinea-pig, a, cells of 

 the vessel; b, stomata or 

 gaps between the latter. 



opening into the .former, has been recognised within the last few years by 

 Recldinghausen, Ludivig, DyWcowsky, Schweigger- 

 Seidel, and Dogiel, corroborating the suppositions 

 of the older observers, as, for instance, those of 

 Mascagni. 



Recklinghausen was the first to point out that 

 the centrum tendineum of the rabbit's diaphragm, 

 is studded with openings whose diameter exceeds 

 that of the red blood-cells, and through which 

 formed particles, such as milk globules and granules 

 of cinnabar, can make their entry, passing into 

 the lymphatics of the diaphragm. This interesting 

 discovery has been confirmed by Schweigger-Seidel 

 andLudwig, in respect to the locality mentioned, and 

 DyHkowsky observed the orifices in question in the 

 intercostal pleura of the dog, and Schweigger-Seidel 

 and Dogiel in the peritoneum of the frog. The fact was also recognised 

 that the lymphatic vessels of serous membranes give off short lateral 

 processes in the direction of the surface (fig. 381, 2, &), which are seen 



to open into the cavities, spoken of by 

 orifices, situated between the epithelial 

 cells [fig. 381, 1 and 3, a, a (3)]. 



Turning now from these finest lymph- 

 atic passages to the larger canals, we 

 observe that the latter have at the com- 

 mencement a precisely similar texture, 

 while their arrangement varies to a great 

 extent, being frequently retiform (fig. 

 382). Here also the walls are formed 

 of nucleated cells alone. The occurrence 

 of scattered nodal and ampullar enlarge- 

 ments is the first striking feature in 

 regard to these canals while still of 

 medium size. In larger trunks the 

 former are more frequently to be seen, 

 in addition to which valves similar to 

 those of veins also present themselves. 



It is only trunks of this kind that 

 can with perfect correctness be called 

 lymphatic vessels. In them at times 

 (however, in smaller branches also), the 

 walls commence to become more and 

 more independent, and to appear distinct, 

 from the surrounding tissues. Here also 

 the relation to the blood-vessels is very 

 different. As a rule, to be sure, lymphatic 

 and blood-vessels run along side by side, 

 but not very rarely we encounter larger 

 lymphatics accompanying a great arterial branch in pairs. They event- 

 ually may lead to an ensheathing of the blood-vessel in a lymph stream, 

 but the latter is of less frequent occurrence than is usually supposed. 



The appearance of new external layers in addition to the cellular tube is 

 a point requiring closer investigation. 



Fig. 381. 1. Epithelium from the under sur- 

 face of the centrum lendineum of the rabbit, 

 a, pores; 2, epithelium of the mediastinum 

 of the dog; a, pores; 3, section through 

 the pleura of the latter animal ; 6, free 

 orifices of short lateral passages of the 

 lymph canals (copied from Ludwig, 

 Schweigger-Seidel, and Dybkowsfy). 



