42 Florence B. Sabin. 



the time, and he has published, with my permission, a valuable recon- 

 struction of my specimen in the Anatomical Eecord for 1912 (Kamp- 

 meier 66). 



The thoracic duct needs to be considered in relation to the veins 

 of the region. Fig. 11 is a section through the seventh cervical verte- 

 bra of an embryo pig 19 mm. long, which is before the thoracic duct 

 begins. There is a complete vascular injection. It will be seen that 

 there is a vascular zone ventral to the vertebra, and from this zone 

 veins surround the sympathetic nerves and enter the dorso-medial 

 border of the internal jugular vein. The esophagus has a plexus of 

 blood vessels in the submucosa, but dorsal to the esophagus is a non- 

 vascular zone of loose connective tissue. The jugular stem of the 

 thoracic duct grows into this non-vascular area dorsal to the esopha- 

 gus, as is shown in fig. 12 from 23a. In this tracing of the section 

 the veins are arbitrarily made black and the lymphatics are shown 

 empty, though in the section the left lymphatic sac and its ducts were 

 injected. The thoracic duct lies in the margin of the vascular zone. 

 As' Kampmeier's reconstruction of this specimen shows, there is a 

 considerable plexus of lymphatics dorsal to the esophagus near their 

 place of origin from the jugular sac. This plexus connects with the 

 left jugular sac in three places. From the injected plexus a short 

 duct follows the left cardinal vein and I think grows to the heart 

 and lungs. A longer vessel crosses to the right side and is the jugular 

 segment of the thoracic duct. This crossing of the duct behind the 

 aorta I have frequently, though not always, noted in older stages. 



The right lymphatic duct curves ventralward and grows to the heart 

 and lungs. Its course is shown in fig. 13 for an embryo 25 mm. long. 

 The asymmetry of the thoracic duct is confined to the jugular portion 

 and corresponds with the asymmetry of the aorta. It is interesting 

 to note that Sala (137, Taf. 14, Fig. 16) and Pensa (101, Taf. 15, 

 Fig. 2) picture a symmetrical thoracic duct in the bird. 



The position of the cisterna chyli has already been shown in figures 

 9 and 10. The cisterna chyli and lower part of the thoracic duct 

 arise in common with the iliac sacs from the mesonephritic veins on 

 either side, as shown in fig. 9. These lymphatic buds from the two 

 sides meet dorsal to the aorta and grow both cerebralward and caudal- 

 ward along the dorsal wall of the aorta. This makes an abundant 

 plexus of blood-filled lymphatics along the course of the abdominal 

 aorta. Any sections of pig embryos of this stage will show that the 



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