Development of the Jugular Lymph Saes. 249 
ple plexiform formation, in line with the fenestrae along the prom- 
ontorial and primitive ulnar areas, and is directly continuous with 
the dorsal veno-lymphatic plexus (fig. 35). The position occu- 
pied by the fenestre in the complex suggest that the latter may 
subsequently be separated into a number of parallel channels 
(see fig. 45). 
Medially, the veno-lymphatic complex of tributary 4 and the 
para-precardinal channel communicates by means of six trans- 
verse branches (a, b, c,d, e andf, figs. 35 and 36) with a large dorso- 
medial somatic trunk (4S) which, as the chief representative of the 
dorsal somatic element of precardinal tributary 4, now enters the 
promontory at the promontorio-precardinal angle and forms the 
first of a series of segmentally arranged promontorial dorsal 
somatic tributaries (4S, 5S, and 6S, figs. 36). The promontorial 
dorsal somatic tributary 7S is not shown in the figure. 
The presence of the above mentioned transverse communica- 
tions at a,b, c,d, e, and f (figs. 35 and 36) represents a stage of 
development in which the separation of the early complex of pre- 
cardinal tributary 4 and its associated para-precardinal channel 
into its veno-lymphatic and dorsal somatic components is still 
incomplete, and more so than on the left side of the embryo, where 
only one such connection exists (A, figs. 33 and 34). 
Fig. 37 is a scheme of the right side of series 138 (fig. 35) viewed 
from its dorsal aspect, in which the dorso-lateral (veno-lymphatic) 
and dorso-medial (somatic) components of tributaries 1, 2,3 and 4 
have been slightly divaricated in order to expose the dorsal sur- 
face of the precardinal and promontory and to emphasize, thereby, 
the double character of the precardinal tributaries, as well as the 
relation subsequently assumed by their veno-lymphatie and 
somatic components with respect to the main venous channels. 
The legends in fig. 37 correspond to those in figs. 35 and 36. 
The following description of the diagram (fig. 37) will make clear 
the complicated conditions observed in series 138. 
In the area of primitive dorsal tributary 4 we encounter, in its 
fullest degree, the development of the dorso-lateral veno-lym- 
phatic component, of the dorso-medial somatic branch, and of the 
transverse communications between the two. The dorso-lateral 
