Development of the Jugular Lymph Saes. 239 
not separated from the postcardinal as far forward on the right 
side (fig. 29) as on the left (fig. 27). In other respects its relations 
to the dorsal sac and the main systemic veins are the same. Figs. 
28 and 30, which represent the medial aspects of the left and right 
sides, respectively, clearly show the relations of the dorsal veno- 
lymphatic plexus and the dorsal somatic tributaries (5S, 6S, 7S 
and 8S) to the promontory and posteardinal vein. In this stage, 
the first of the promontorial dorsal somatic tributaries is the fifth 
of the entire precardino-postcardinal series (5S). 
In a subsequent stage the fourth of the entire series (4$) is the 
first promontorial branch (compare figs. 28 and 30 with fig. 45). 
In the embryo at present under consideration tributary 4, as a 
whole, is still included, together with the para-precardinal channel, 
in a common plexus, which will subsequently differentiate into a 
veno-lymphatic portion (para-precardinal channel plus veno- 
lymphatic component of 4) and into a somatic element. The 
former will constitute the caudal division of the ventral veno- 
lymphatic plexus. The latter, as the somatic component of tri- 
butary 4, will enter the promontory as the first of the promontor- 
ial dorsal somatic tributaries (4S) in line with the rest of the series 
(5S, 6S, 7S,) and independently of the caudal division of the ven- 
tral veno-lymphatic plexus. 
This ontogenetic transferal of the fourth dorsal somatic tribu- 
tary to the promontory is illustrated diagrammatically in figs. 8, 9, 
10, 11 and 114A, and is further explained in detail in dealing with 
series 138 presently to be considered. As stated above the dorsal 
somatic tributaries (5S, 6S, etc.), of the promontory do not enter 
into the formation of the veno-lymphatic plexus. 
The embryo also exhibits well the early disposition of the veno- 
lymphatic plexus to shift distinctly to the dorso-lateral circum- 
ference of the precardinal and promontory, while the somatic 
tributaries are grouping themselves into a regular series entering 
the dorso-medial aspect of the promontory. 
