LYMPHATIC SYSTBM OF SKIN AND MUCOUS MEMBRANES, 387 
cleft or channel, or terminate with a cecal extremity, as is 
the case in some papille (see below). As a general rule we 
find the majority of the vessels of the most superficial stratum 
larger than those of the middle layers, and these again 
smaller than those of the deeper sections. I1 cannot 
agree with Teichmann, Neumann, and others, that the 
lymphatics are arranged asa superficial and deep plexus, 
than that those of the fegmer are finer and their plexus 
denser than that of thedeeper. I maintain, on the contrary, 
that throughout the thickness of the skin there are hori- 
zontal plexuses of lymphaties, of course with oblique or even 
vertical connecting branches; that the vessels of the super- 
ficial layers are larger than those of the middle layer; and 
that there is no absolute difference in the density of the 
plexuses, for the vessels are tolerably densely arranged in 
all layers, but relatively less so in the deeper strata, owing 
to the interposition of the sweat glands and the hair bulbs. 
16. As regards the shape and nature of these vessels they 
appear more or less tubular, but many of them, and this 
refers to all layers, including the papillary stratum, are 
irregular, since they show isolated saccular dilatations, or 
appear through a succession of them, more or less varicose.” 
In all layers very fine vessels are seen to join tubes many 
times larger, and one and the same vessel, if followed for a 
distance, may be seen to change its calibre. In these respects 
the lymphatics comport themselves like those of other organs. 
Following in a horizontal seetion under a higher power the 
outline of some vessels, especially of those that run out 
freely into the tissue, it, viz. the outline, will be found not 
quite smooth, but showing from place to place minute dis- 
continuities and irregularities, which give the vessel a more 
or less crenate appearance. This has been observed also by 
Schenk ; its significance will be explained later on. 
All lymphatics are lined with a single layer of elongated 
endothelial plates, and in this respect they do not differ 
from other lymphatics. Besides this endothelium there is 
no other tissue which can be called their own, except 
the trabecule of the ground substance forming their outer 
support. 
17. Teichmann, as well as Neumann, maintain that only 
the lymphatics of the deep subcutaneous plexus are pos- 
sessed of valves. ) 
G. and F. Hoggan ascribe such also to their “ dermic” 
vessels, that is, to those extending as horizontal and vertical 
sets of vessels through the whole thickness of the skin. - 
I agree in this respect with G, and F, Hoggan, inasmuch 
