130 



NORMAL HISTOLOGY. 



cavity (Fig. 30) ; but they may be demonstrated also in the tissues 

 of man and of the higher animals : the central tendon of the dia- 

 phragm, on which they were first discovered in the peritoneum by von 

 Recklinghausen, offers a favorable place for their study. In addition 

 to the stomata occurring in the peritoneum covering the diaphragm, 

 similar apertures have been observed in the omentum, the pleura, and 

 the pericardium. The stomata, either directly 

 or through minute canals, lead into the sub- 

 jacent lymphatic vessels and are surrounded 

 by cuboidal or spherical guard-cells. 



The stroma of the serous membranes con- 

 sists of interlacing bundles of white fibrous 

 tissue, mingled with elastic fibres, which are 



^7^^^" *^^SZ? <Z*zZ ' - -"^ 



especially numerous in the more superficial 

 Peritoneum in section from p arts wne re they frequently form a reticular 



dog: /, peritoneum proper, . ^ 



consisting of endotheiium of layer. 1 he interstices between the fibrous 

 free surface and subendotheiiai bundles are occupied by the ground-sub- 



fibrous stroma containing net- , , - . . 



work of elastic fibres ; *, sub- stance ; the latter after a time in some cases, 



peritoneal vascular connective as m {he omentum, Suffers local absorption, 



interfascicular orifices then partially taking its 



place. The serous membrane, which in its earlier condition forms a 

 continuous sheet, may become riddled with apertures, and is said to 

 be fenestrated. Where the ground-substance and stroma are well 

 developed and of considerable thickness, particularly in the vicinity 

 of folds, adipose and sometimes lymphoid tissue occur in addition to 

 the blood-vessels and lymphatics. The ground-substance in places 

 where dense is penetrated by an intercommunicating system of 

 lymph-spaces opening into the lymphatic vessels of the serous 

 membrane. Branched connective-tissue cells are also frequently 

 seen with processes extending between the endothelial plates of the 

 free surface ; such processes when stained with silver probably form 

 the pseudo-stomata already mentioned ; other protoplasmic exten- 

 sions of the cells may come into relation with the walls of the blood- 

 vessels or of the larger lymphatics. 



The subserous layer, where well developed, is composed of 

 loosely-arranged bundles of fibro-elastic tissue, between which blood- 

 vessels and lymphatics, with migratory leucocytes, are situated. 



The blood-vessels of serous membranes contribute wide-meshed 

 net- works both to the layer of proper stroma and to the subserous 

 tissue ; in positions where tracts of adipose or of lymphoid tissue 

 exist, the capillaries form net-works enclosing the fat-sacs or the 

 lymphoid masses. 



The lymphatics of serous membranes are very numerous, and are 

 represented by the definite lymphatic vessels and the lymph-spaces 



