Development of the Jugular Lymph Sacs. 267 
Series 102, 8.5" Embryo 
Reconstruction of left side 
b 
Medial aspect, fig. 45 
This view of the reconstruction shows three tiers of elongated 
fenestrae and deep depressions on the medial surface of the caudal 
division of the ventral veno-lymphatic plexus which appear to 
divide it into four parallel channels. Taken by itself this view 
of the reconstruction suggests that this portion of the plexus has 
been formed as the result of a fusion between four parallel vessels. 
Such is not the case, however, since the ontogenetic history of 
this plexus proves conclusively that these parallel vessels are 
secondarily formed as the intervals between the fenestral spans 
developed in the plexiform anlage of this structure. 
The medial view of the reconstruction also shows the extensive — 
and dilated character of the promontory and the relations which 
it holds to its dorsal somatic (4S, 5S, 6S, and 7S, fig. 45) and 
veno-lymphatic structures (Cf. also fig. 43). 
Series 102, 8.5"”" Embryo 
Reconstruction of right side, 
Lateral aspect, fig. 46 
As on the left side of this embryo the three primary divisions 
of the veno-lymphatic plexus are fully established on the right 
side. 
I. VENTRAL VENO-LYMPHATIC PLEXUS 
1. Cephalic Division 
The precardinal dorsal tributary 1 (1 VL) is represented by a 
dilated, elongated and fenestrated sac which has retained its pri- 
mary connection with the precardinal. It has not yet fused at 
its base with the adjacent veno-lymphatic components (2 VL, 
3 (VL, and in this respect both sides of this embryo agree. In 
addition to its contribution, at its base, to the ventral plexus, this 
veno-lymphatie component of tributary 1 (1 VL) will, by its 
further dilation and caudal extension, fuse with the dorsal veno- 
