Development of the Jugular Lymph Saes. 211 
sions of the veno-lymphatic plexus are well shown in series 102, 
fig. 46. 
Second Mode of Development. In this form the dorso-lateral 
circumference of the straight segment of the precardinal, in the 
area included between the levels of the first and third dorsal 
somatic tributaries (1, 2 and 3, in fig. 8), retains the plexiform con- 
dition and by continued growth and enlargement of the inter- 
reticular spaces forms a multi-fenestrated appendage to the main 
venous channel (cephalic division of ventral veno-lymphatic 
plexus in fig. 9). By confluence of these fenestral spaces this 
appendage is separated as a veno-lymphatic sac from the definite 
vein except at its cephalic end, where one or two of the primary 
connections between the veno-lymphatic structure thus formed 
and the precardinal vein proper persist until a later stage, serving 
as channels for the evacuation of the blood from the veno-lym- 
phatic sac into the definite venous system, after the three primary 
veno-lymphatic plexuses have fused to form a common sac. The 
tributaries, 1, 2 and 3 (1, 2 and 3, in fig. 9) appear to be taken up 
as a whole in this veno-lymphatic development and to lose their 
individual character. 
2. Development of the Caudal or Posterior Division of the Ven- 
tral Veno-Lymphatic Plexus. 
This portion of the ventral veno-lymphatic plexus is also formed 
in one of two ways: 
1. From part of primary dorsal tributary 4 (4, fig. 8), combined 
with a portion of the precardinal vein which, between the early 
terminal of 4 and the promontory, crystallizes out of the plexi- 
form network of the primary vein along its dorso-lateral cireum- 
ference as a “‘para-precardinal channel”’ (figs. 8, 9 and 10). 
2. From the para-precardinal channel alone. In this case 
tributary 4 is not involved directly in the veno-lymphatic process 
and remains in its entirety as a dorsal somatic branch secondarily 
entering the promontory. 
In the early venous stages (fig. 8), as mentioned above, the 
fourth dorsal tributary of the precardinal (4) is by far the largest 
