The Origin and Development of the Lymphatic System. 29 



The blood vessels show a great development. The five spinal seg- 

 mental veins are clear, draining the large plexuses around each spinal 

 ganglion; the ganglia are now farther ventralward than in the pre- 

 ceding stage. The superficial capillary plexus shows the mosl marked 

 changes. There is a continuous sheet of superficial capillaries in the 



L s 



A cv 



Fig. 6. — Section through the third segmental vein in an injected embryo 

 pig which measured 11 mm. in its greatest diameter. The section, which is 

 250 |U thick, shows the relation of the jugular lymphatic sprouts or buds 

 to an anterior cardinal vein. Magnified about 40 times. The blood vessels 

 were injected with India ink through the umbilical artery. The lymphatic 

 sprouts. L. s., have a natural injection of blood; these lymphatic sprouts lie 

 in a non-blood-vascular zone dorso-lateral to the anterior cardinal vein. 

 A. c. v. = vena cardinalis anterior; g — groove. 



neck, anastomising with the branchial vessels, with the pericardia] 

 vessels and with the abundant capillary plexus of the arm hud. 

 Opposite the medulla the connections of this superficial plexus with 

 the anterior cardinal vein are very numerous, while opposite the heart 

 a lew veins connect ii either directly with the anterior cardinal vein 

 or more frequently with the main segmental branches. It is this 



