DEVELOPMENT OF THE JUGULAR LYMPH SAC 481 



anastomosed to form a longitudinal channel situated lateral to 

 the vertebral anlagen. As a final consideration of this stage, 

 a view of the lateral group of channels, especially those connected 

 with or situated near the precardinal vein, gives the impression 

 that they are leading toward the formation of a longitudinally 

 arranged plexus, which will be situated dorsal to the cardinal 

 line. These channels are obviously of venous origin and are 

 undoubtedly homologous with the veno-lymphatic vessels in the 

 mammalian embryo as exemplified in a cat embryo of 7 mm. 

 (Huntington and McClure, figs. 33, 34, 35, 36) . 



Chick embryo of six days. Reconstruction, right side. Fig. Jf-. 

 The medial or dorsal somatic group of vessels is not represented 

 in fig. 4- The changes between the preceding stage of devel- 

 opment (chick embryo of five days and ten hours) and the one 

 under consideration here have affected principally the lateral 

 group of vascular elements (5). The medial and lateral groups 

 have now become completely separated and are absolutely inde- 

 pendent of each other. Whatever communication existed in 

 the 5-day-and-lO-hour stage has been wholly dissolved, the medial 

 group now constituting the dorsal somatic vessels exclusively, 

 the lateral group (5) forming a large and complicated plexus of 

 channels which calls .for further observation and interpretation. 



The vascular channels which, in the preceding stage (fig. 3, 5), 

 occupied a position dorsal to the proximal ends of the precardinal 

 and postcardinal veins, have enlarged into an enormously com- 

 plicated plexus (fig. 4, 6) which no longer possesses the former 

 fairly distinct segmental character, has become entirely separated 

 from the dorso-medial somatic tributaries, and has further lost 

 the previous rather free communication with the cardinal veins, 

 being now entirely detached from the main venous trunks with 

 the exception of a single small anterior capillary connection. The 

 plexus is relatively shorter than that of the previous stage, being 

 confined for the most part to the region of the duct of Cuvier (5) 

 and the proximal end of the precardinal (1) and extending but a 

 short distance along the postcardinal line (2). It also extends 

 farther around on the lateral aspect of the precardinal. The com- 

 ponent channels have a general longitudinal trend, and vary in 



