40 



Florence R. Sabin. 



D. THE THORACIC DUCT IN THE PIG. 



The thoracic duct is easy to inject after it is once fully formed, 

 but in the early stages exceedingly difficult. In later stages it can be 

 injected indirectly either from the retroperitoneal sac or from the iliac 

 Moreover it lies in the edge of the wall of the aorta, which guides 



sac 



the needle for a direct injection. In the lower thoracic region it 

 forms such an abundant plexus around the aorta that if the needle 



Pig. 11. — Section through the 7th cervical vertebra of an embryo pig 

 measuring 19 mm. Magnified 45 times. The blood vessels have been injected 

 with India ink through the umbilical arteries. This is the stage just pre- 

 ceding the development of the thoracic duct. B. v. p. = plexus of blood 

 vessels ventral to the vertebra; E. = esophagus; J. 1. s. = jugular lymph 

 sac; N. s. = nervus sympathetica ; T. = trachea; V. j. i. = vena jugularis 

 interna. 



avoids the azygos vein it is almost certain to enter lymphatics. Pensa's 

 (105) series of injections in different forms, as well as fig. 7 (Heuer 

 43), show that it is a constant characteristic of the lower thoracic part 

 of the duct to be a complete plexus around the aorta, while the upper 

 thoracic portion consists of one or two ducts. 



The thoracic duct forms from two places: (1) a duct which grows 

 downward from the left jugular sac, and (2) a plexus which buds 

 out from the mesonephritic veins and completely surrounds the aorta. 



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