Development of the Jugular Lymph Sacs. 225 
through the tributary branches, repeating, on a small and serial 
scale, the phenomena observed in the development of the jugular 
promontory at the site of the principal venous confluence of this 
region, the promontory representing in its inception a correspond- 
ing enlargement of the main vein, as yet indistinctly indicated, at 
the junction of pre- and posteardinal veins to form the duct of 
Cuvier. 
These early stages offer a characteristic irregular and redundant 
appearance of the embryonic vein channels, which in part are 
but poorly differentiated against the surrounding tissue, a con- 
dition likewise characteristic of the ventral and dorsal tributaries 
of the main vein. In place of the more clearly defined series 
‘of collateral branches of the succeeding stages, the earlier embryos 
offer a number of short and more or less irregalar branches, which, 
in their aggregate, represent the single more fully formed tribu- 
tary of the later stages. 
This appearance is due to the numerous secondary capillary 
vessels which develop around both the main vein and its tribu- 
taries, and which subsequently give rise, as above stated, to the 
fenestrated character of the channels, and to the appearance of the 
veno-lymphatic anlages. 
In the following description of the dorsal tributdries of the 
caudal or straight segment of the precardinal, the assignment of 
a complex of several branches to the valuation of one of the single 
tributaries of later stages is based primarily upon the latter’s rela- 
tion tothe localized enlargements of the precardinal into which 
the tributaries of earlier stages open. The increased vascularity 
of the tissues, and the resulting augmentation of the number of 
capillary vessels found in the area of each of the principal tribu- 
taries, is one of the phenomena preceding and directly leading up 
to the fenestral process above described as active in producing the 
veno-lymphatic condition. This secondary capillary reticulum 
to a certain extent masks the individuality of the primary pre- 
cardinal tributaries. We have evidence that a localized group 
or complex of tributaries which opens dorsally into the precardinal 
vein in early stages may be represented by a single well-defined 
branch in later stages. We also have positive evidence that this 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 10, NO. 2. 
