18 ANATOMY OF THE LYMPHATIC SYSTEM. 



to form tracts, and that they project generally only over one surface 

 of the membrane. The larger ones are provided with a special system 

 of more or less numerous capillary blood-vessels. They are to be 

 met with also here, either along the larger blood-vessels, or isolated 

 at those points to which a number of thin connective-tissue trabe- 

 culse radiate. The older the animal the larger and more numerous 

 nodules are to be found, and the thicker and longer are the tracts 

 they form. In young animals, their number is very limited, and 

 they are of so small a size that they are to be recognised only under 

 the microscope. 



Before considering their minute structure, we wish to call the 

 attention of the reader to the following points : All these nodular 

 and cord-like structures we have referred to in this chapter belong, 

 if I may so say, to the proper ground-substance of the membrane. 

 We have seen in the first chapter that the germinating endothelium 

 may form small nodular bodies on the surface of the membrane, 

 olf the surface of the nodular structures previously 

 mentioned. 



If we look at a very small, that is a very young nodule, which 

 can only be discovered under the microscope as such, and is isolated 

 in the fenestrated membrane, we find in a pencilled silver-stained 

 preparation, in which, like in those we have described in the rabbit's 

 omentum, the ground-substance has remained nearly perfectly un- 

 stained, whereas the cellular elements are distinctly visible by their 

 yellowish or brownish granules, we find, I say, also here, that the 

 ground-substance contains more or less flat branched-protoplasmic 

 cells with oblong nuclei. These cells are more or less crowded 

 together, and join one another by their processes to form a network. 

 The nucleus is generally single, and contains one or two nucleoli ; 

 sometimes the nucleus is constricted, or even divided into two. 

 Migratory cells are also to be found in these places, which either 

 resemble lymphoid cells, or which are large and coarsely granular. 

 There is one point which we need merely allude to here, having 

 entered into it fully in speaking of the rabbit's omentum, viz. that 

 some of the larger migratory cells form a distinct continuum with 

 one of those branched cells, by means of a longer or shorter neck, that 



