10 



/,'. Sabin. 



I I. I in I HOB U IC DUCT in THE PIG. 



The thoracic duel is easy to inj.it after it is <'u*<' fully formed, 

 but in the early - dingly difficult. In later Btages it inn be 



injected indirectly either from the retroperitoneal sac or from the iliac- 

 sac. Mon over it lies in the edge of the wall of the aorta, which guides 

 or a direct injection. In the lower thoracic region it 

 forms such an abundan! plexus around the aorta that if the m 



w ^ 



Fig. 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 

 Bac; N. b. = nervus sympathetica ; T. = trachea; V. j. i. = vena jugularis 

 interna. 



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

 i L05) series of injections in different forms, as well as fig. i (Heuer 

 t.3), show thai n ostanl characteristic of the lower thoracic part 



of the duct i" 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 duel which grows 

 downward from the left jugular 3ac, and (2) a plexus which buds 

 out from the mesonephritic veins and completely surrounds the aorta. 



