Development of the Jugular Lympn Saces. 233 
cumference of the caudal part of the precardinal. In series 47 
(4, fig. 26), the precardinal end of this element appears as the large 
single trunk entering the precardinal in the same situation. The 
formation of tributary 4, with its cephalic and caudal tributary 
a and b, in series 30 (figs. 22 and 23), has already been considered 
in detail, and corresponds evidently to a further development in 
these later embryos of the conditions presented by the earlier 
series. 
(b) Postcardinal 
The redundant plexiform area of the postcardinal (H) corre- 
sponding to the dorsal aspect of the Cuvierian junction in series 
30 and 31, and representing the early anlage of the dorsal veno- 
lymphatic plexus is already well indicated in both of the earlier 
stages. In series 134 (fig. 25) it is represented by the dilated and 
fenestrated anterior blind end of the posteardinal (H). In series 
47 (fig. 26), it appears as the fenestrated and plexiform append- 
age of the dorsal circumference of the postcardinal (7) just caudal 
to the latter’s entrance into the duct of Cuvier. 
INTERMEDIATE EARLY STAGES OF PRE- AND POSTCARDINAL 
VENO-LYMPHATIC DEVELOPMENT 
Series 109, 6.2" Embryo 
Series 2, 7” Embryo 
Series 188, 7"”" Embryo 
Series 18, 7.25"™" Embryo 
Figs. 27 to 39 
A. GENERAL CONSIDERATIONS 
The main venous trunks have now begun to assume the arrange- 
ment typical of the later stages. 
The cephalic arched segment, conforming to the increased 
cranial flexure of the embryo, has turned ventro-caudad, present- 
ing a well-defined convexity, which receives the most anterior 
dorsal tributaries (A-B). 
The straight precardinal segment, shortened anteriorly by the 
