ANATOMY OF THE ALIMENTARY CANAL. 
461 
rarely show a nucleus. These bodies, by their processes, form a continuous network 
(or reticulum), the epithelial cells being contained in the meshes. 
This reticulum stains very deeply in gold or hsematoxylin ; and in oblique sections it 
can be demonstrated that the dark line which is present below the epithelium in vertical 
sections is due to the presence of these bodies, i. e. of the reticulum. 
The same structures will be observed in a cross section of the epithelial cells of a 
Lieberkuhn’s crypt (see Plate 39. tig. 5, where the reticulum is seen to send processes 
horizontally round the epithelial cells as well as downwards to join with the reticulum of 
the mucosa). Thus the bodies forming the dark line are anatomically continuous with 
the reticulum of the mucosa, and are the uppermost layer of that reticulum. This can 
also be well seen in an oblique section of a villus, where we can similarly trace the 
continuity of the reticulum which surrounds the epithelial cells with the reticulum of 
the substance of the villus. 
There is, however, a difference between the reticulum which is found among the 
epithelial cells and that which elsewhere pervades the mucous membrane, inasmuch as 
the nodes of the reticulum surrounding the epithelial cells are very broad, and the 
reticulum itself is very delicate, and this gives the appearance of small cells with 
branching processes (see Plate 40. fig. 4). 
Membrana Propria, of the Villi, and of the processes of the Mucous Membrane of the 
Large Intestine. 
For a long time I conceived that the dark line below the epithelium was the membrana 
(r, figs. 10 & 13, Plate 39) ; this was found not to be the case. In the colon large cells 
were seen to be situated below the dark line (see fig. 10) ; but there was no evidence 
in these preparations that they formed a membrane. On examining, however, some 
sections of the villi of a monkey, which were denuded of their epithelium, it was noticed 
that the villi are bordered by large cells with oval nuclei, that these cells are placed 
more or less closely together, and have somewhat the character of endothelial plates. 
In places these cells were found to form a membrane ; this was seen if the cells were 
separated from the mucosa and viewed from above (see Plate 40. fig. 6). We notice in 
the figure that some of the capillary blood-vessels are attached to the membrane ; this 
is always found to be the case. And we further notice that the membrane has gaps or 
holes in it. We can show that these gaps or holes are not artificial products, if we 
compare the section with others prepared and stained in exactly the same manner 
(see figs. 6, 7, 8). Fig. 7 shows the membrana of a Lieberkuhn’s crypt; fig. 8 gives 
the appearances of two alveoli of the mammary gland : neither in fig. 7 nor in fig. 8 is 
there any indication of holes in the membrane. 
In these preparations of villi, devoid of epithelium and bordered by large cells, the 
dark line which is generally seen at the base of the epithelial cells can nowhere be 
found ; and this teaches us that the reticulum forming the dark line at the base of the 
epithelium always breaks off with the epithelial cells, that its connexions with the 
epithelial cells are much more intimate than with the rest of the villus. 
