ORIGIN OF LYMPHATICS. 



185 



Fig. 12f 





Fig. 125. — LvjirHATic Vessels 



OF THE SKI>f OF THE 



Breast injected (after 

 Brescliet). 



a, superficial, and 6, deeper 

 plexus ; c, a lymphatic vessel, 

 which i^roceeded to the axil- 

 lary glands. 



phatic trunks. In certain structures, such as the skin, the plexuses 

 consist of several strata, becoming finer as they approach the surface, 

 in respect both of the calibre of the vessels and the closeness of their 

 reticulation,, as is shown in figure 125. But even the most superficial 

 and finest network is composed of vessels 

 which are larger than the sanguiferous 

 capillaries. 



The short anastomosing branches of these 

 plexuses are often of very unequal size, even in 

 the same stratum, some being dilated and 

 almost saccular, whilst others immediately 

 communicating with these are narrow, so 

 that the network may assume a varicose 

 character (see fig. 124). In some situations 

 the plexuses have much the appearance of 

 strata of intercommunicating cavities, and a 

 characteristic example of this appearance is 

 afforded by the intestine of the turtle after 

 its Ij'mphatics have been injected with mer- 

 cury ; these vessels are then seen to emerge 

 from what has all the appearance of a dense 

 stratum of small rounded saccules filled 

 with mercury and lying beneath the surface of 



the mucous coat. This appearance, however, is produced by the short 

 distended branches of a very close lymphatic network. 



Here and there vessels are seen joining the plexuses of origin which 

 arise in the tissue by a blind and often irregular extremity. A long- 

 known and well-marked example of such a mode of commencement is to 

 be found in the lacteals of the intestinal villi, which, although they form 

 networks in the larger and broader villi, arise in others by a single 

 vessel beginning with a blind or closed extremity at the free end of the 

 villus, whence it sinks down to join the general plexus of the intestinal 

 membrane. 



Lacunar. — In the lacunar mode of origin of the lymphatics, which 

 was shown to exist in the testis by Ludwig and Tomsa, and has since 

 been described in some other glandular organs, the lymphatic vessels 

 proceed from irregular or shapeless spaces in the internal parts ; the 

 spaces, that is, which intervene between the several structures of which 

 the organ is composed. Thus, in a gland, they are the spaces which 

 lie between or surround the blood-vessels, secreting tubes or saccules, 

 partitioning or inclosing membranes, and the like. Though shapeless, 

 or at least of no regular form, these anfractuous cavities are limited and 

 defined by a layer of flattened epithelioid cells, agreeing in character 

 with those of the lymphatic vessels. It may be presumed that their 

 opposite sides are in apposition or in near proximity, as in serous mem- 

 branes, for the lymph deposited in these recesses is not suffered to 

 accumulate, but is drained off by the lymphatic vessels which lead out 

 of them. 



Indeed, as will be pointed out further on, the serous cavities them- 

 selves may in a certain sense be looked upon as large lymph lacuna?, 

 for it has been shown that in various parts they communicate directly 

 with lymphatics by means of definite apertures. 

 In some of the lower animals the lacunar condition of lymphatics has been 



