390 LYMPHATIC SYSTEM. 



substance or by processes which are sent up to the surface of the membrane from 

 more deeply lying cells (pbeudostomata of Klein and Burdon-Sanderson) : the larger 

 ones, on the other hand, are true apertures (slomata), which are surrounded by a 

 ring of small cubical cells (fig. 449, s, s'), and open into a subjacent lymphatic 

 vessel, either directly or by the medium of a short canal lined with similar cells. 

 The surface cells of the serous membrane are not everywhere uniform in size, but 

 patches are here and there met with in which they are smaller and more granular in 

 appearance and it is in these parts that the stomata and pseudo-stomata are more 

 frequently seen (figs. 448, 449). The epithelium-cells of the membrane often 



Fig. 448. PORTION OF ENDOTHELIUM OF PERITONEUM FROM THE UNDER SURFACE OF THE RABBIT'S 



DIAPHRAGM. (Klein.) 



a, larger cells ; 6, smaller ones, with here and there a pseudostoma between. 



present a somewhat radiated aspect near the stomata, the silver lines converging 

 towards the orifice. According to Klein, it is not unfrequent to find evidences of 

 proliferation, especially in the neighbourhood of the stomata and pseudo-stomata, 

 cells being met with containing two or even many nuclei, and others which are 

 being budded off from the cells of the membrane. Since, however, these statements 

 depend on observations which were made before the importance of the karyokinetic 

 figures as a guide to cell-multiplication was recognised, it is important that they 

 should be repeated. 



The stomata were discovered in the peritoneal covering of the central tendon of the dia- 

 phragm by Recklinghausen, who found that milk-globules could be made to pass through them 

 into the lymphatics. Similar apertures were found by Ludwig and Dybkowsky in the pleura 

 of mammals, and by Schweigger-Seidel and Dogiel in the septum between the peritoneal 

 cavity of the frog and the great lymph-sac (cisterna magna) behind it. They have since been 

 discovered on the omentum by Klein, and have also been recognised in the pericardium. 



The substance of the membrane underneath the endothelium is composed of a 

 connective tissue ground-substance in which is a variable amount of fibres, both 

 white and elastic ; the latter in many serous membranes, as remarked by Henle, are 

 principally collected into a reticular layer near the surface. The bundles of white 

 fibres are also arranged in a reticular manner, frequently uniting with one another, 

 and the meshes of the reticulation which they form are occupied by the ground- 

 substance of the membrane, and bridged over by the flattened cells of the general 



