454 



OTTO F. KAMPMEIER 



Fig. 24 Transverse section through the upper thoracic region in a 23 mm. pig 

 embiyo (injected series, slide 15, section 11), X 100. 5d, right thoracic duct 

 anlage injected; Ex, extravasations of the injection mass from the right duct- 

 anlage into the loose surrounding mesenchyme ; 5s, left thoracic duct anlage ; lid, lis, 

 right and left postcardinals injected; 13, aorta; 17, oesophagus; 25, branches of 

 the postcardinals injected. 



As shown in figures 22, 23, 25 and 26, at the beginning of the 

 lymphatic phase the thoracic duct in transverse section resembles 

 a condensed plexus and may be said to be at the height of its 

 complexity. For from now on there is a gradual reduction of 

 this condition until the two limbs of the thoracic duct exist nor- 

 mally as single simple channels. By the breaking down of the 

 abundant tissue bridges which had divided its channel into a 

 labyrinth of loculi, the ducts assume more and more the appear- 

 ance of unobstructed tubes. In figure 27, taken from a 26 mm. 

 embryo, the outlines of the ducts (5d, 5s) are assured, and only 

 the vestiges of former septa and trabeculae are still visible here 

 and there in the form of few small tissue spurs and filaments pro- 

 jecting into the cavities. 



The most startling change, however, occurs in the precardinal 

 division in the region of the jugular lymph sac. The reader will 



