612 LYMPHATIC SYSTEM. 



property of rapid absorption on all the mucous and se- 

 rous membranes, and on all the other tissues of the body, 

 by their quickly conveying the transuded matters to the 

 circulating blood, and they become exquisitely sensitive in 

 the inflamed state. They commonly exhibit two distinct 

 coats, an outer dilatable fibrous tunic, and an inner smooth, 

 less elastic, serous coat which forms internal crescentic folds 

 or semilunar valves. The valves are commonly in pairs, 

 directed towards the heart, less numerous than in the lacteals, 

 and apparently deficient in some of the viscera, as the lungs, 

 the liver, and the uterus. The anastomoses of the lympha- 

 tics are much more frequent than those of the veins, which 

 occur much oftener than in the arteries ; they probably com- 

 mence by closed orifices, like the tubuli of glands. The lym- 

 phatics form numerous so-named conglobate glands or gan- 

 glions, consisting of plexiform sub-divisions convoluted into 

 small tubercles, with afferent and efferent lymphatics leading 

 to and from these pseudo-glands, like the nervous filaments 

 in sympathelic ganglia ; and muscular pulsating cavities are 

 sometimes developed on the lymphatics, like the pulsating 

 sacs on the sanguiferous system of many invertebrata. 



In the class of fishes, where the existence and the extensive 

 distribution of the lymphatics have been long known, they 

 have been observed in almost every form of osseous and car- 

 tilaginous species, excepting in the lowest cyclostome fishes, 

 as the myxine and the lampreys, but they have not been 

 detected in the invertebrated tribes, where their function, 

 like that of the lacteals, appears to be performed by the 

 sanguiferous capillaries. The lymphatics of fishes were early 

 examined and described by Monro, Hewson, Fohmann, 

 Meckel, and others, who injected them with fluids, inflated 

 them with air, and pointed out their yet simple structure, 

 apparently consisting of a single very thin tunic, their want 

 of internal valves, excepting at their entrance into veins 

 where there are generally valves, their distribution throughout 

 the textures and organs of the body, especially over the super- 

 ficial parts, and their supposed free communications with the 

 venous system. Instead of the distinct compact conglobate 

 glands presented by this system in the warm-blooded classes, 

 we here observe occasional groups of crowded tortuous 

 anastomosing lymphatics, presenting a kind of analysis of 



