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TEXT-BOOK OF EMBRYOLOGY. 



develops more rapidly than the one on the right and becomes the thoracic duct. 

 The lymphatic vessels to the various organs probably grow out as branches 

 of the thoracic duct and follow the courses of the arteries. A similar outgrowth 

 produces the lymphatics of the extremities. It may be said, generally, that 

 during development, as in the adult, the deep lymphatic vessels have a ten- 

 dency to follow the arteries, the superficial ones to follow the veins. 



Ant. cardinal vein 

 Subclavian vein 



Post, cardinal vein , 

 Diaphragm. 



Suprarenal gland.- 

 Mesonephros 



Kidney 



Ant. lymph heart 



Deep lymphatics 



of arm 



Branches to heart 



\"\" Branches to lung 

 - Aorta 



Branch to oesophagus 

 Branches to stomach 

 -- -Branch to duodenum 



Branches to mesenteric plexus 

 ' Cisterna chyli 



Post, lymph heart 



Deep lymphatics 

 to leg 



FIG. 254. Diagram showing the arrangement of the lymphatic vessels in a 

 pig embryo of 40 mm. Sabin. 



While not admitting that the lymphatic vessels arise independently in the 

 mesenchyme, one investigator * in his work on the rabbit asserts that they take 

 origin not merely from the four centers which have been mentioned in the 

 preceding paragraphs, but may evaginate from veins at many points, lose their 

 connection with the veins, anastomose in the mesenchyme, and then acquire 

 their permanent communications with the veins secondarily. 



The most recent investigations f again seem to indicate that the lymphatic 

 vessels are not primarily connected with the veins, but arise independently in 



* Lewis. f Huntington and McClure. 



