THE LYMPHATIC SYSTEM. 223 



areas of the skin (ear, tip of nose, toes) and in the meninges, kid- 

 ney, etc. 



The blood-vessels, and more particularly the arteries, possess a 

 rich nerve supply, comprising both nonmedullated and medullated 

 nerves. The nonmedullated nerves, the neuraxes of sympathetic 

 neurones, the cell-bodies of which are situated as a veiy general 

 rule in some distant ganglion, form plexuses in the adventitia of the 

 vessel-walls ; from this, single nerve-fibers, or small bundles of such, 

 are given off, which enter the media and, after repeated division, 

 end on the involuntary muscle-cells in a manner previously de- 

 scribed. (See p. 166 and Fig. 133.) Through the agency of these 

 nerves, the caliber of the vessel is controlled. They are known as 

 vasomotor nerves. Quite recently Dogiel, Schemetkin, and Huber 

 have shown that many vessels possess also sensory nerve-endings. 

 The medullated nerve-fibers terminating in such endings, branch 

 repeatedly before losing their medullary sheaths. These nerve-fibers 

 with their branches accompany the vessels in the fibrous tissue 

 immediately surrounding the adventitia. The nonmedullated ter- 

 minal branches end in telodendria, consisting of small fibrils, beset 

 with large varicosities and usually terminating in relatively large 

 nodules. 



The branches and telodendria of a single medullated nerve-fiber 

 (sensory nerve) terminating in a vessel are often spread over a 

 relatively large area, some of the branches of such a nerve often 

 accompanying an arterial branch, to terminate thereon. In the 

 large vessels, the telodendria of the sensory nerves ajre found not 

 only in the adventitia, but also in the intima, as has been shown by 

 Schemetkin. (Seep. 215.) 



B. THE LYMPHATIC SYSTEM. 



\. LYMPH-VESSELS. 



The larger lymph-vessels the thoracic duct, the lymphatic 

 trunks, and the lymph-vessels have relatively thin walls, and 

 their structure corresponds in general to that of the veins. They 

 possess numerous valves, and are subject to great variation in cali- 

 ber according to the amount of their contents. When empty, they 

 collapse and the smaller ones are not easily distinguished from the 

 surrounding connective tissue. Tiraofeew and Dogiel (97) have 

 shown that the lymph -vessels are supplied with nerves, which in 

 their arrangement are similar to those found in the arteries and 

 veins, though not so numerous. The latter, who has given the 

 fuller description, states that the nerves supplying the lymph- 

 vessels are varicose, nonmedullated fibers which form plexuses sur- 

 rounding these structures. The terminal branches would appear 

 to end on the nonstriated muscle cells found in the wall of the 

 lymph -vessel. 



