i38 SEEOUS MEMBEANES. 



be brought into view by treatment with nitrate of silver. The lines of 

 junction of the cells which are thus made evident, may be straight and 

 even, but are most commonly slightly jagged or sinuous. Here and 

 there between the cells apertures are to be seen, which are of two 

 kinds. The smaller of these, which are also the more numerous, are 

 occupied by processes which are sent up to the surface of the mem- 

 brane from deeper lying cells (pseudostomata, fig. 132) : the larger, on 

 the other hand; the stomata, are true apertures, which are surrounded 

 by a ring of small cubical cells (fig. 127 s, s\ page 189), and open into 

 a subjacent lymphatic vessel, either directly or by the medium of a 

 short canal lined with similar cells, as already mentioned in treating 

 of lymphatics. The surface cells of the serous membrane are not 

 everywhere uniform in size (see figs. 127 and 132), but patches are 

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

 in appearance. It is not unfrequent also to find evidences of prolifera- 

 tion, especially in the neighbourhood of the stomata and pseudostomata, 

 cells being met with containing two or even many nuclei (Klein). 



The substance of the membrane underneath the epithelioid layer is 

 composed of a connective tissue ground substance in which are a 

 variable amount of fibres, both white and elastic ; the former, when 

 there are two or more strata, take a difTerent direction in the difiFerent 

 planes ; the latter unite into a network, and, in many serous mem- 

 branes, as remarked by Henle, are principally collected into a reticular 

 layer near the surface. The ground substance contains the blood- 

 vessels and lymphatics of the membrane, as well as a large number' 

 of flattened connective tissue corpuscles with their corresponding cell- 

 spaces (fig. 133), which are often collected into epithelioid patches. 

 In parts of the membrane in which these corpuscles are more thinly 

 scattered, they possess branching processes, some of which intercom- 

 municate with those of neighbouring cells, whilst others, as before 

 said, pass up to the surface of the membrane (pseudostomata), and 

 others again, become connected to the walls of the lymphatics and blood- 

 vessels (see fig. 126, p. 187). 



Blood-vessels ending in a capillary network with comparatively 

 wide meshes pervade the subserous tissue and the tissue of the serous 

 membrane. 



The lymphatics of the serous membranes are exceedingly abundant. 

 Their relation both to the cell-spaces of the tissue and to the surface 

 of the membrane, as well as their general arrangement, has been 

 already noticed (pp. 18 G — 191). They are sometimes met with ensheath- 

 ing the blood-vessels. 



Nodules occur here and there in the substance of the serous mem- 

 branes which consist of a close network of branched connective tissue- 

 cells amongst which are a number of lymphoid cells or leucocytes, 

 similar to the pale corpuscles of the blood. These nodules, the 

 larger of which have a rich supply of blood-vessels, are developed in 

 connection with the lymphatics, being formed either around those 

 vessels, or actually within them, in which case the cells forming the 

 walls of the lymphatic vessel exhibit processes which project into the 

 interior and join with the enclosed retiform tissue. The cells of this 

 tissue are in fact developed by a proliferation of the flattened cells of the 

 lymphatic, which is of course considerably enlarged at these spots. 

 These lymphatic nodules (peri and endo-lymphangial nodules of Klein) 



