ANATOMY OF THE ALIMENTAEY CANAL. 
465 
Not only does the reticulum surround the endothelium, hot we can also show that it 
penetrates between the individual endothelial cells. This is seen if we examine a 
longitudinal section of a broad vein, and view the inner surface of the vessel from above : 
see Plate 40. fig. 19, where we find a delicate reticulum between the individual cells. Nor 
must we be surprised that the reticulum is very delicate, as it has been shown that mem- 
branes, when viewed from the surface and separated from the rest of the tissue, show 
no trace of the reticulum (see figs. 6 & 7), although in oblique sections of these mem- 
branes in situ (as in Plate 39. fig. 5), as we have seen, it is quite easy to demonstrate a 
reticulum among the separate endothelial cells. 
It has already been mentioned that the cells of the membrana propria partially 
surround the superficial capillaries. 
The Character and Relations of the Chyle-vessels of the Villi. 
In the cylindrical villi the central canal is somewhat club-shaped, the lower end 
being much narrowed. The villi of the hedgehog are best adapted to demonstrate the 
chyle-vessels in sections, as in that animal they are very large, and are not surrounded 
by many involuntary muscle-fibres. 
The walls of the chyle-vessels are composed of endothelial plates. The relation of 
the reticulum to the chyle-vessels is almost exactly similar to its relation to the veins ; 
i. e. y in longitudinal sections of the vessel, threads are seen attached to the wall, which 
are continuous with the reticulum of the mucosa (see Plate 41. fig. 22), whereas, on 
viewing the vessel from above, there is seen to be a delicate reticulum penetrating 
between the endothelial plates (see fig. 20). 
If the chyle-vessel be cut rather obliquely, as in fig. 21, we notice that the reticulum 
surrounding the cells of the mucosa is continuous with that which envelops the endo- 
thelial plates. This specimen was drawn from a villus situated above Brunner’s glands 
in the dog : it will be seen that in the upper part of the chyle-vessel the cells of the 
villus and the endothelial plates of the chyle-vessel are continuous. 
In sections of the cylindrical villi, if the cells of the tissue have been accidentally 
removed, threads of the connective-tissue reticulum are seen attaching the upper 
widened end of the chyle-vessel to the membrana (see Plate 39. fig. 14). 
The Tissue composing the Mucosa. 
The mucous membrane contains no fibrous tissue. Probably the involuntary muscle 
fibres, with their intervening -threads of reticulum, have been mistaken for it. 
The mucosa is everywhere composed of a reticulum and of cells held in its meshes. 
Wherever the intestine contains lymphatic follicles, it can be shown that the reticulum 
of the follicles is continuous with that of the rest of the mucosa ; and there are many 
places in the mucosa where the cells contained in the meshes of the reticulum are only 
lymph-corpuscles. 
What, then, is the tissue of a villus ? Is it the same as that of the rest of the mucosa, 
as is often assumed 1 And is the tissue of the mucosa the same as that found in a follicle 
MDCCCLXXVI. 3 T 
