Development of the Jugular Lymph Sacs. 261 
speaking, this para-precardinal channel, in this instance, as well 
as in all others, in which it serves as a portal through which tribu- 
tary 4 drains into the promontory, must be regarded as constitut- 
ing a portion of tributary 4. In addition to its points of communi- 
eation with the precardinal and promontory, just mentioned, the 
veno-lymphatic component of tributary 4 (4VL, fig. 41) also 
communicates with its companion dorsal somatic component (4S, 
fig. 41) near the point where the latter opens into the promontory, 
a circumstance which betrays the common origin of these two com- 
ponents from the primary dorsal plexus of tributary 4 of earlier 
stages (see figs. 1/A, 35 and 37). The small diverticular-shaped 
process which projects ventrad from the para-precardinal channel 
(AP, fig. 41) corresponds to a similarly situated process on the left 
side of series 138 (fig. 33). 
In front of the primary point of connection of tributary 4 with 
the precardinal (X in fig. 41) the latter receives a small inverted 
L-shaped tributary (Z in fig. 41) which opens into its dorso-lateral 
circumference. This small vessel is probably related to the plexus 
of the primary terminal of tributary 4 (X) from which it has been 
separated in the condensation of the channels. Its position with 
respect to the main channel establishes its veno-lymphatic character 
and indicates that it will enter into the formation of the ventral 
division of the veno-lymphatic plexus as in series 102, fig. 44. 
The dorsal veno-lymphatic plexus was only partially recon- 
structed on the right side of this embryo and, therefore, will not be 
considered. 
Reconstruction of Left Side, Lateral Aspect, Fig. 42. 
A comparison of the right and left sides of this embryo affords 
an interesting illustration of the unequal chronological development 
of the three main divisions of the veno-lymphatic plexus which may 
occur upon opposite sides of the same embryo. On the left side 
(fig. 42) the cephalic division is much advanced in development 
and the caudal division of the ventral plexus extremely rudimentary, 
while on the right side (fig. 41) the reverse conditions obtain. 
The anlage of the external jugular vein is well developed and 
opens into the promontory. 
