ON THE LYMPHATIC SYSTEM. 161 



liain (see above) as to the other l)'mphatics. These are best 

 developed in glands in which the connective tissue is present in 

 considerable quantity, such as the parotid of the dog and ape, 

 the submaxillary of man, ape, and also of the dog. Injecting 

 Berlin blue into the interlobular connective tissue, the injection 

 matter readily passes into the lymphatics, and on suitably pre- 

 pared sections it can be ascertained that the lymphatics are 

 arranged as two sets of vessels : (a) lymphatic vessels belonging 

 to, or surrounding the ducts, and {d) lymphatic vessels belong- 

 ing to, or surrounding the blood-vessels, both arteries and veins. 

 In both sets we have to do with real lymphatic tubes, whose 

 wall, like that of the vessels in other similar organs, is a single 

 layer of endothehal plates of an elongated shape, and with more 

 or less sinous outlines. The vessels are possessed of valves and 

 corresponding saccular dilatations ; they are very irregular in 

 thickness, for very minute tubes are seen suddenly to become 

 distended into broad sinuses. 



The vessels surrounding the ducts, as well as those surround- 

 ing the blood-vessels, form rich anastomoses, but they are chiefly 

 extending in a direction parallel to the duct and blood-vessels. 

 The vessels of both sets anastomose with one another. Where 

 the amount of the connective tissue in which the ducts and large 

 blood-vessels are embedded is great, as in the above-named 

 glands, the double arrangement of the lymphatic vessels, viz. as 

 those of the ducts and those of the blood-vessels, is easily ascer- 

 tained ; but this is not the case in those glands in which the 

 connective tissue is scanty; even in the former glands tracing 

 them with the duct and blood-vessels into the individual lobules, 

 the vessels of the two sets become naturally so reduced in 

 number and so compressed in space that this double arrange- 

 ment is lost. 



As regards the vessels surrounding the ducts, their arrange- 

 ment and nature is easily understood on a reference to the 

 figures. That some of them are possessed of valves there can 

 be no doubt about, from the inspection of the respective pre- 

 parations. 



Amongst the lymphatics of the second set, i.e. the perivas- 

 cular lymphatics, there are also some of them that are possessed 

 of valves. Their relation to the blood-vessels is various ; either 

 the lymphatics follow the blood-vessels surrounding them as a 

 plexus, or the latter, both arteries and veins, appear surrounded 

 by a lymphatic for a greater or smaller portion of their circum- 

 ference, as is shown in fig. 13 ; or the blood-vessel is completely 

 ensheathed in a lymphatic. One of the most striking examples 

 of this kind is to be found in the sublingual gland of the guinea- 

 pig. At the side of, and close to the large nerve branch (of the 



VOL. XXII. NEW SER. L 



