ANATOMY OF SEROUS MEMBRANES. 145 



"With respect to the endothelium of the lymphatic vessels 

 and capillaries, we have nothing to add to what has been 

 taught by Recklinghausen. 



The cellular tissue-elements of the pleural serous membrane 

 are in general flat and branched. Two layers of them may be 

 distinguished ; that which is more superficial lies immediately 

 under the endothelium of the surface. The cells are sometimes 

 large flat bodies lying close together so as to be only slightly 

 branched, and appearing to be separated by linear intercellular 

 substance which only here and there forms nodular elevations. 

 In this case, the appearance presented is as if these were under 

 the endothelium of the surface another layer of large flat- 

 tened endothelial cells. This appearance is met with in the 

 vicinity of the vena cava and aorta as well as in isolated spots 

 of the middle line of the anterior quadrant of the centrum ten- 

 dineum. On the other hand, the most superficial tissue- 

 cells may sometimes be clearly branched and united by means 

 of their processes. When these two types of formation are 

 in contact, evidently transitional forms may be seen. 



Tlie cells of the deeper layer which are imbedded in the 

 tissue of the serosa are smaller than those just mentioned, 

 and are also for the most part flattened and more or less 

 branched. They are connected with the superficial layer at 

 several points. In the vicinity of the lymph-capillaries of 

 the pleural serosa they are often approximated in such a way 

 that they touch each other only in a line, two, three, or four 

 together, or else they are grouped round a common centre. On 

 the side by which they are not in contact with one another, 

 they nevertheless have processes by which they are connected 

 with the neighbouring isolated cells. The nearer, generally 

 speaking, they are to the lymph-capillaries, the less branched 

 and the more closely approximated are they. Finally, they 

 may be seen to be directly continuous with the endothelium 

 of the lymph-capillaries, that is, to stand in direct commu- 

 nication with these vessels. The same relations subsist 

 between the flat, more or less branched cells, situated in 

 the outermost parts of the tendinous fasciculi, and the cell 

 networks found in some of the fissures on the one hand, as 

 well as on the other hand between the former cells and the 

 endothelium of the vessels of the fissures.^ 



The same relations may be demonstrated for the abdominal 

 as for the pleural serosa, in places where the former is not 

 perforated by fenestrated openings. For the system of 

 spaces in which the cellular structures already mentioned 



1 See Dr. J. M. Bi'uce's researches on the "Structure of Tendon," made 

 under the direction of Dr. Klein, in this Journal, p. 129. 



