208 The Blood-Supply of Lymphatic Vessels in Man 
lacteal wall, though in these largest vessels, in places, capillary loops and 
meshes are seen superficial to the plane of the chief plexus. These supply 
the outermost connective tissue and fat, but appear never to form another 
well-defined layer of capillaries such as exists in the sheaths of the 
larger blood-vessels. 
It will be well here to refer to the actual place of the vasa vasorum in 
the lymphatic wall. Seen in section these are always adventitial in posi- 
tion. Occasionally a capillary twig underhes a few muscle fibers, but it is 
even then in a small septum of connective tissue, as shown by a Van Giesen 
stain. Such stains show clearly the remarkable proportion of the lacteal 
wall taken by the muscular media. Fig. 13 shows a typical section of 
these ducts in man. From within outward one notices the characteristic 
projection of the endothelial nuclei into the lumen, the slight subendo- 
thelial tissue (barely demonstrable), the strong media, the vasa vasorum, 
and finally, the connective tissue and fat of the adventitia. The absence 
of much subendothelial tissue and the presence of so strong a media, are 
probably characters peculiar to the human lacteals, but the adventitial 
position of the lymphatic vasa vasorum seems a general fact. In this 
respect, then, the lymphatic trunks resemble the arteries rather than the 
veins, whose media is copiously supphed with nourishing vessels. 
The chief facts brought forward in this paper may briefly be summed 
up as follows: 
1. Lymphatic vessels possess a special blood-supply when possessing a 
caliber far below that of blood-vessels which have vasa vasorum. 
2. The lymphatic vessel is typically supplied along one or two axes by 
long-accompanying arteries and veins which give off a capillary plexus. 
3. This capillary plexus is truly adventitial in character but rests 
directly on the muscular media, in this respect resembling that of the 
arterial walls. 
4. The plan of circulation is essentially the same in all ducts above a 
medium caliber, though the capillary mesh is closer in the larger vessels. 
5. Whether the supply is unilateral or bilateral, an accommodation in 
the extent and size of the arterial and venous vasa vasorum is made in 
accordance with a capillary bed of uniform length. 
It is a pleasant duty to express here my thanks to Professor Mall. 
I must acknowledge, also, the very kind assistance of Mr. Broedel, under 
whom a portion of the drawings were made. 
