336 COMMENCEMENT OF THE ABSORBENTS. 



of the valve which is next to their termination, and this occa- 

 sions their knotted appearance when they are injected. The 

 object of this valvular structure seems to be the prevention of 

 retrograde motion of the contained fluid, in consequence of 

 lateral pressure. 



Where the different trunks of the absorbents open into the 

 veins, there are one or two valves to prevent the regurgitation 

 of the blood into them. 



The valves of course prevent the injection of the branches 

 of these vessels from their trunks. In some animals the valves 

 have sometimes been ruptured, or forced back ; and the absorb- 

 ents have been injected in a retrograde direction. There are 

 but two or three instances upon record where this has been 

 practicable In the Human Subject. 



In consequence of the impracticability of injecting the small 

 branches from the larger, the absorbent vessels cannot, gene- 

 rally, be demonstrated at their commencement, or origin. It 

 is, however, to be observed, that the Lacteals, or Absorbents 

 of the Intestines, appear no way different from other absor- 

 bents ; and they have been seen distended with chyle, from 

 their commencement, in certain subjects who had died sud- 

 denly. Their origins have been described very differently by 

 different observers. 



Mr. Cruikshank describes them as originating on the sur- 

 faces of the villi, by a number of very small radiated branches 

 with open orifices ; which branches soon unite to form a 

 trunk. 



Lieberkuhn believed them to commence in the form of an 

 ampuUula. (See page 42 of this volume.) 



The second Monro also believed that the absorbents began 

 by very small tubes, with open orifices in several species of 

 fish.* 



It is stated by Dr. Soemmering, upon the authority of Haase, 



a German anatomist, that when mercury is forced backwards in 



the absorbent vessels of the foot and the heart, it has sometimes 



escaped on the surfaces of those parts. The probable inference 



* See his work on the Structure and Physiology of Fishes, p. 34. 



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