EXPLANATION OF PLATES. 

 Plate 1. 



Fig. 1 . Diagram of transverse section of left linig of an embryo pig 3 cm. long, in which the l)l()()d-ve.ssels were injected 

 through the umbilical artery with india ink. The lymphatics appear as dilated spaces (blue). The sec- 

 tion is 20/i thick and is stained with hematoxylin and eosin, aurantia, and orange G. X55. Ao, aorta; 

 T, trachea. 



Fig. 2. Diagram of section through loljule of lung of an embryo pig 7 cm. long, in whi<-h the lymphatics were injected 

 with india ink through the left tracheal plexus. The veins were slightly injected by the rupture of a 

 lymphatic ves.sel into a vein near the hilum. The section is lOO/j thick and is unstained. X47.5. 

 A, artery; B, bronchus, V , vein; I'l, pleura. 



Fig. 3. Surface of lung of an embryo pig cm. long, in which the lymphatics were injected with india ink through 

 the left tracheal plexus. The section was taken from the ventro-lateral surface of the left lower lobe 

 and is about 200^ thick and is unstained. X29.4. P L, primary lobule. 



Fig. 4. Longitudinal section of lung of an embryo pig 6 cm. long, in which the lymphatics were injected with india 

 ink through the left tracheal plexus. The \ eins contain some blood pigment. The section is 400m thick 

 and is vmstained. X33. 1', vein; B, bronchus. 



Fig. .5. Diagram of left tracheal plexus in an embryo pig 6 em. long, in which the lym])hatics were injected througli 

 the thoracic duct. Cleared by Spalteholz method. Note that i)art of the vessel marked with an 

 asterisk (*) has been removed in dis.secting the body-wall away. This ves.sel is the one described as 

 the first to the lung. X15. *, first vessel to lung; T, trachea; Th D, thoracic duct; L T P., left 

 tracheal plexus; Ao, aorta. 



Plate 2. 



Fig. 1. Dissection of an embryo pig 4 cm. long, in which the lymphatics were injected with prussian blue through the 

 retroperitoneal sac. The heart, aortic arch, left lung, and the body-wall have been removed. Cleared 

 by the Spalteholz method. X19. Th D, thoracic duct; R Th D right thoracic duct; R T P, right 

 tracheal plexus; L T P, left tracheal plexus; C L, cardiac lymphatics; Ao, aorta; B, bronchus; Oe, 

 esophagus. 



Fig. 2. Section of a small area of the lung of an embryo pig 7 cm. long, in which the lymphatics were injected with 

 Prussian blue through the retroperitoneal sac. Drawing to show the relation of the peri-bronchial 

 lymphatics to the wall of the bronchus. Section is 20 >i thick and is stained with hematoxylin and eosin, 

 aurantia, and orange G. X93. B, bronchus. 



Fig. 3. Dissection of an embryo pig 4 cm. long, in which the lymphatics were injected with prussian blue through 

 the retroperitoneal sac. The left lung, the arch of the aorta, the pulmonary artery, and the body-wall 

 have been removed. Cleared by the Spalteholz method. The left tracheal plexus is shown as a solid 

 blue ma.ss because the meshes are so close that they could not be analyzed in the drawing. X15. Th I), 

 thoracic duct; R Th D, right thoracic duct; Ao, aorta; L T P, left tracheal plexus; B, bronchus. 



Fig. 4. Longitudinal section of upper lobe of right lung of an embryo pig 6 cm. long, in which the lymphatics were 

 injected with prussian blue through the retroperitoneal sac, and the veins were injected with india ink 

 through the pulmonary vein. The section is 400 fi thick and is unstained. Cleared by the Spalteholz 

 method. X3f). 



Plate 3. 



Fig. L Small block of an embryo pig 15 cm. long, in which the lymphatics were injected with prussian blue by ])unc- 

 ture of an interlobular septum. The arteries were injected with india ink through the inilmonary artery. 

 Cleared by the Spalteholz method and mounted in balsam. The specimen was mounted at a convenient 

 angle to best show the interlobular septum ; unfortunately, it was jarreil out of posit ion while being drawn 

 and hence the group of lymphatics in the septum is .shown bent to one side. X40. PI, pleura; A, 

 artery; / L .S', interlobular septum. 



Fig. 2. Diagram of a dissection of an embryo pig 3 cm. long, in which both the right and left jugular sacs were injected 

 and, from them, the right and the left thoracic ducts respectively. India ink was used. The body-wall, 

 heart, and left lung have been removed. Cleared by SpaUeholz method. X30. Th D, thoracic duct; 

 R Th D, right thoracic duct; V C S, vena cava superior; Ao, aorta; /' A, pulmonary artery; C L, car- 

 diac branch of the right thoracic duct. 



Fig. 3. Diagram of a section of the right lung of an embryo pig 6 cm. long. This is the same specimen from whicli 

 figure 4, plate 2, was made; the part of the section shown in that figure is indicated by an X. X20. 



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