508 



PHYSIOLOGY 



CHAP. 



241). It can be shown by the method of double staining with 

 silver nitrate and carmine that there is a perivascular lymphatic 

 space between the peripheral layer of the sheath and that which 

 adheres to the surface of the blood-vessels ; that slender connecting 

 filaments or lamellae pass between the two layers ; that the wavy 

 epithelioid plaques of the external layer are continued on to the 



FIG. 240. Frog's interdigital membrane, with injected blood and lymph vessels. (Ranvier.) 

 .->-, Network of blood capillaries;- II, network of lymph capillaries ; pp, pigment cells. Mag- 

 nification, 50 diameters. 



internal layer, and also invest the connecting lamellae. Where 

 the blood-vessels are much increased in size, they perforate the 

 lymphatic sheath, and the two kinds of vessels run distinct from, 

 but alongside, one another. In certain of the lower animals, 



FIG. 241. (Left.) Artery of frog's mesentery, enclosed in perivascular lymphatic, which is 

 stained with silver nitrate, to show the outlines of epithelioid cells. (Klein.) 



FIG. 242. (Right.) Aorta of tortoise, enclosed in large perivascular lymphatic. (Gegenbaur.) 

 Numerous filaments of connective tissue are seen, connecting the blood-vessel with the 

 lymphatic. 



however, e.g. in the frog, the larger vessels are also surrounded by 

 lymphatic sheaths, as also the aorta in the tortoise (Figs. 241, 242). 

 Rusconi (1845) was the first to describe the perivascular lymphatic 

 sheath. 



(c) Outside the lymph capillaries also, in every part of the 

 body, and more particularly where there is loose connective tissue, 

 a labyrinth of lacunae or interstices of the most varied forms 



