STRUCTURE OF THE ABSORBENT VESSELS. 335 



their progress to these large vessels, pass through certain bodies 

 which have been denominated Conglobate Glands, and may 

 be considered as appendages of the absorbent system. 



The absorbent vessels are composed of two coats, which are 

 thin, but dense and firm, and also elastic* The coats of the 

 thoracic duct may be separated from each other. The internal 

 surface of the exterior coat is fibrous. The internal coat is a 

 delicate but strong membrane. There is great reason to 

 believe that the above mentioned fibres are muscular, or at 

 least contractile ; for the absorbent vessels have been observed, 

 by Haller, to contract upon the application of strong sulphuric 

 acid. They have also been observed to propel their contents 

 with considerable rapidity, by their own contraction, inde- 

 pendent of pressure, or of motion communicated by any other 

 body. 



Blood-vessels are sometimes observable in the coats of the 

 larger absorbents, in injected subjects. The vascularity of 

 these tubes may also be inferred from the inflammation which 

 frequently takes place in them. 



Nerves have not been traced into their texture ; but the 

 absorbents seem to be painful when they are inflamed, and, 

 therefore, it is probable that they are supplied with nerves. 



The absorbent vessels are very generally supplied with 

 valves, which are much more numerous in some of them than 

 in others ; and are different in their number, in the same 

 vessels, in different subjects. 



Very frequently there are several valves in the course of an 

 inch : sometimes a valve will not appear in the course of 

 several inches. In the Thoracic Duct the number of valves is 

 very different in different subjects. These valves are folds or 

 plaits of the internal membrane, and are of a semicircular form. 

 There are commonly two of them together originating from 

 opposite sides of the vessel. 



The absorbents are generally somewhat dilated on the side 



* Microscopical observers find in addition to these a third coat, placed on the 

 inner face of the second which they call the epithelial lining. — p. 



