CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 29 



sometimes find elements which appear like nobs on the branched cells 

 of the lymph-canalicular system, and which perfectly resemble lymph 

 corpuscles. A fact we have had already opportunity to refer to is 

 that near the large blood-vessels similar smaller or larger masses of 

 branched cells are to be found which mostly form oblong nodules and 

 cords, which begin now to have a special system of blood-vessels of 

 their own. These nodules and cords are exactly like those described in 

 the omentum, namely, those which we described under the name of 

 perilymphangial nodules and tracts. Their intimate structure, their 

 migratory cells, the relation of these to the branched cells of the 

 matrix, the relation of these nodules to fat tissue, is here exactly the 

 same as in the omentum. Especially worthy of notice is the fact 

 that in guinea-pigs I have met with mesenteries which exhibited an 

 immense development of these perilymphangial tracts, whereas in 

 cats and dogs the perilymphangial tracts have a great tendency to 

 convert themselves into fat tracts. 



As regards the cellular elements of the abdominal serosa of the 

 centrum tendineum, there is very little to be said. They differ in no 

 respect from those we have found in the mesentery : where the larger 

 blood-vessels branch, and where, as we shall see, lymph-capillaries 

 are to be found forming a network, there we find also that the 

 branched cells of the serosa are situated nearer to each other. 

 Amongst those we find also here groups of flattened cells, which are 

 connected with each other only by very few short processes, or even 

 touch each other end to end. In correspondence with this arrange- 

 ment, the lymph-canalicular system also becomes modified, namely, 

 contains groups of lacunae, which communicate with each other by a 

 few very short canaliculi. The cells of the pleural serosa of the 

 centrum tendineum can be recognised more easily on pencilled silver 

 preparations than those of the abdominal serosa. We there see, close 

 under the endothelium of the surface, a layer of very large flat, 

 branched cells, which lie mostly isolated, but in the neighbourhood of 

 those places where the vena cava and aorta pass through the dia- 

 phragm, and also in the median portions of the centrum tendineum, are 

 found in larger groups closely together, so that in many places there 



