DEVELOPMENT OF THE JUGULAK LYMPH SAC 475 



this plexus condenses further to form a ' sponge-hke' (schwanun- 

 artig) structure which is comparable with the posterior lymph 

 heart. He does not state that these venous derivatives break 

 away from the veins and coalesce still further to form a definite 

 sac which subsequently acquires a new connection with the veins. 



The present investigation is based upon a study of serial sec- 

 tions of chick embryos and reconstructions made after a slight 

 modification of Born's wax plate method. The embryos were 

 fixed in vom Rath's picro-sublimate-acetic mixture and the sec- 

 tions stained with Delafield's hsematoxylin and picric acid, or 

 fixed in Zenker's or Bouin's fluid and stained with Weigert's 

 hsBmatoxylin and orange G. 



Chick embryo of five days and twenty hours. Reconstruction, 

 right side. Fig. 1. The precardinal vein {1) pursues a compara- 

 tively straight course from the cephalic arch to its junction with 

 the postcardinal {2). The postcardinal, after receiving the 

 primitive ulnar vein at the level of the upper limb bud, extends 

 cephalad along the side of the aorta for some distance and then 

 bends ventrad rather abruptly to join the precardinal. The con- 

 fluence of the two cardinal veins forms the duct of Cuvier {3) 

 which bends ventrad and caudad to open into the sinus venosus. 

 The sharp bend in the postcardinal, just caudal to its union with 

 the precardinal, produces a fairly distinct promontory in the car- 

 dinal line. 



So far as can be determined in this embryo, no intersegmental 

 veins (4) open into the precardinal {!). The intersegmental 

 veins (4) which are distinctly formed empty into the postcar- 

 dinal {2). Four of these which are especially large open upon 

 the dorso-cephalic side of the above mentioned promontory; 

 the others open into the more nearly straight portion of the post- 

 cardinal {2) at regular intervals as far back as the confluence of 

 the latter vein with the primitive ulnar, 



■ In the tissue dorsal to the straight portion of the precardinal 

 vein (-?), a collection of vascular islands {5) is situated in a man- 

 ner which indicates the inception of a plexus of vascular channels. 

 In addition to these islands, there are a few short channels which 

 communicate with the precardinal. In the region of and caudal 



