432 



OTTO F. KAMPMEIER 



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Fig. 10 Transverse section through the upper thoracic region in a 20 mm. pig. 

 embryo (series 194, slide 26, section 21), X 150. 4-d, potential lymphatic anlage in 

 the right thoracic duct line; 4-s, lymph space in the left duct line; 7, oblique vessel, 

 here plexiform; 8, dorsal segmental vein; 10, left precardinal; 13, aorta; 17, 

 oesophagus. (Reconstruction, fig. 29.) 



the territory formerly traversed by the temporary venous plex- 

 uses. 



In series 194 (20 mm. embryo) the atrophy of the oblique ves- 

 sel (7) and its replacement by lymphatics has begun anteriorly, 

 where it is supplanted to a greater or lesser degree by perivenous 

 spaces (4-d, fig. 29) which reflect the features of those further for- 

 ward but are smaller and less conspicuous by reason of the greater 

 simplicity of the vessel replaced. Along the second half of its 

 course lymphatic anlagen are met with which are not formed in 

 such intimate relations but lie ventral to and not closely in contact 

 with it. Figure 10 illustrates a section from this region. The 

 clear area (4-d) subjacent to the plexiform oblique vessel (7) in 

 the triangular or wedge-shaped territory between the aorta and 

 the oesophagus unhesitatingly suggests a thoracic duct anlage in 

 the making, as an examination of its character and a comparison 

 with later stages seem to affirm. That this clear area is less com- 



