ANATOMY OF THE ABSORBENT SYSTEM. 285 



filamentous appearance more deeply, which has been considered 

 as fibrous, or muscular, by some anatomists, owing to its con- 

 traction upon the application of certain stimulants. The inter- 

 nal membrane is extremely fine and perfectly transparent? and 

 is remarkable for its frequent duplications, whereby a system 

 of valves is produced resembling those of the veins. These 

 valves are generally of a semi-lunar or parabolic shape, and are 

 arranged in pairs, though according to Lauth,* some of them are 

 circular, and do not close the canal entirely. The pairs are not 

 placed at stated distances from one another, but vary in differ- 

 ent parts of the body ; in some places there are several in the 

 course of an inch, and in others not one pair. As a general 

 rule, they are less frequent as the trunk increases in magni- 

 tude; hence, the thoracic duct has but very few of them. The 

 valves, by having their semi-circumference fixed, while the dia- 

 meter is loose and inclined in the course of the circulation, pre- 

 vent the retrograde movement of the contained fluid. The en- 

 largement of the trunk at their outer face into sinuses, resem- 

 bling those at the valves of the veins, gives also to the lympha- 

 tic trunk the knotted condition when it is fully injected. 



The coats of the lymphatic vessels, though very thin, are yet 

 dense and extremely strong, much more in proportion than 

 those of any other tubes. They are both extensible and elas- 

 tic, possess striking powers of spontaneous contraction in the 

 living body, and also in the dead, but to a less extent. They 

 are furnished with arteries arid veins, and probably with nerves 

 also, from their sensibility in a state of inflammation. And, as 

 they stand in need of a similar organization with other canals, 

 their parietes are said also to have lymphatics. 



The absorbent vessels are, by some, divided into lacteals and 

 lymphatics,! the first term expressing those which convey the 

 chyle from the intestines, and the second such as are found in 

 other parts of the system. As the difference is more in the 

 fluid conducted than in the structure of the vessels themselves, 



* Loc. cit. 



t This division has been handed down from the time of Bartholine, who, not 

 suspecting the absorbing powers of the lymphatics, held them only as organs of 

 circulation for restoring to the heart the serum of the blood. The sagacious 

 mind of the late Dr. W. Hunter first imagined their absorbing powers, and esta- 

 blished the theory of their identity of function, in this respect, with the lacteals. 

 The priority of the theory was vrarmly contested for Dr. Monroe, of Edinburgh, 



