SEROUS MEMBHAXES. 



389 



branes are perfectly closed sacs, inasmuch as it has two openings by which the 

 Fallopian tubes communicate with its cavity. 



A serous membrane sometimes lines a fibrous membrane, as where the serous 

 layer of the pericardium adheres to its outer or fibrous part. Such a combination is 

 often named a fibro-serous membrane. 



The inner surface of a serous membrane is free, smooth, and polished ; and, as 

 would occur with an empty bladder, the inner surface of one part of the sac is 

 applied to the corresponding surface of some other part ; a small quantity of fluid, 

 usually not more than merely moistens the contiguous surfaces, being interposed. 

 The parts situated in a cavity lined by serous membrane, being themselves also 

 covered by it, can thus glide easily against its parietes or upon each other, and their 

 motion is rendered smoother by the lubricating fluid. 



The outer surface most commonly adheres to the parts which it lines or covers, 

 the connection being effected by means of areolar tissue, named therefore "subserous," 

 which, when the membrane is detached, gives to its outer and previously adherent 

 surface a fiocculent aspect. The degree of firmness of the connection is very various : 

 in some parts the membrane can scarcely be separated ; in others its attachment is 

 so lax as to permit easy displacement. 



Structure and properties. Serous membranes are thin and transparent, so 

 that the colour of subjacent parts shines through them. They are tolerably strong, 



Fig. 447. EKDOTHELIAL LATER OF OMEKTUM OF RABBIT. 



(E. A. S.) 



NITRATE OF SILVER PREPARATION. 



with a moderate degree of extensibility and elasticity. They are lined on the inner 

 surface by a simple epithelial layer of flattened cells (endothelium, fig. 447), each of 

 which contains a round or oval nucleus with one or two nucleoli, and an intranuclear 

 network. The cells have, according to Klein, a comparatively coarse network of 

 minute fibrils embedded in the otherwise clear cell-substance. The outlines of the 

 cells may readily 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, which are also 

 the more numerous, are occupied either by an accumulation of the intercellular 



