56 DKVKI.oi'MKN r OK THK LYMI'lIATiCS OF Tllli LLXCS IN TlIK EiMBUYO PIG. 



of which anastomose with those mentioned above as growing down into the hilum 

 of the hmg from the i)iilmonary hmb of the right duct. Other vessels turn outwards 

 along the bronchi and veins and grow into \\w lung-tissue of the ujiper lobe. This 

 process will be described later. 



Along the right duct, cephalad to the division into the two branches, other 

 vessels are given off; some grow down to anastomose with ascending branches Ij'ing 

 along the tracheal wall and coming from the vessels described above, while others 

 grow to the tracheal wall at varying i)ositions along the section h'ing between the 

 jugular anastomosis and the bifurcation, corresponding somewhat to the vessels 

 on the other side, with which their branches anastomose, forming the tracheal 

 supply. The earliest injection of the lymphatics of the right side were at 2.8 and 

 2.9 cm. 



Figure 2, plate 3, shows an embryo of 3 cm., where the injection was made into 

 the right sac, which illustrates the relative position of the vessels to the upper right 

 lobe and the limb that follows the vena cava to the heart. This drawing is diagram- 

 matic and does not show the different vessels to the lobes on the right side, though 

 some of them were injected. The left duct is shown without an,y branches. 



In figure 1, plate 2, the right tracheal plexus is represented. Though it is very 

 incomplete, it shows the general form of the plexus and its relation to the similar 

 jilexus on the other side. The right tracheal plexus, in its simplest form, consists of 

 a few vessels which are beginning to anastomose along the lateral wall. These 

 anastomoses become more and more complex and numerous imtil, along the right 

 side of the trachea, a plexus somewhat similar to that of the other side is formed. 

 They differ, however, in that on the right there is no aortic arch to complicate the 

 form. Thei'(>fore the plexus is a simple sheet-like group of vessels which lie along 

 the lateral wall of the trachea, but do not extend up over the ventral surface of the 

 bifurcation, except by a few anastomosing vessels. It anastomoses freely with the 

 larger plexus from the other side on the ventral surface of the trachea, and later the 

 combined plexuses lose their individuality and appear continuous. In the meantime 

 the two tracheal plexuses have begun to anastomose. This will next be described. 



Between 3.3 and 4.5 cm. the two tracheal plexuses anastomose by means of 

 numerous vessels which grow around the trachea, both dorsally and ventrally. 

 Above the level of the aortic arch these connecting vessels are far less numerous 

 than below, where the two are m(n-ged into a sheet-like i)lexus that surrounds the 

 trachea and passes down into the lungs as tubes of vessels surrounding the bronchi. 

 Above the liifm'cation the dorsal surface of the trachea has fewer vessels than the 

 ventral, while the two original lateral plexuses are much more closely meshed, 

 representing the anlagen of the two lateral groups of lymph nodes of the adult. 



From the close-meshed i)lexus on the left side of the trachea just at the bifur- 

 cation a grouji of lymphatics pass up over the left stem bronchus and sweep across 

 to the right bronchus, forming the ujiper group of vessels lying on the bronchial wall. 

 These grow down on the side and anastomose with the vessels coming down from 

 the plexus on the right side. Thus it will l)e seen that the left supply is a more 

 imi)ortant part of the general origin than the right, supplying, as it does, all of the 

 left lung and part of the right. 



