Development of the Jugular Lymph Sacs. 215 
Later Veno-lymphatic Stage (figs. 12, 18, 14 and 19). 
The separation of the veno-lymphatie (lateral) and somatic 
(medial) components of tributary 4 has been completed. Each 
component now obtains a separate and independent entrance into 
the main venous channel. 
The para-precardinal channel has further separated from the 
main vein and has fused with the veno-lymphatic element of tribu- 
tary 4(4VL) into asingle sac (figs. 13, 14and 19), to form the caudal 
division of the ventral veno-lymphatic plexus which is now no 
longer connected by transverse anastomoses with the somatic 
portion (48) of tributary 4. 
The above outlined plan of development for the caudal division 
of the ventral veno-lymphatic plexus, appears to be more or less 
uniform in character for cat embryos, in general, in which the 
para-precardinal channel and tributary 4 combined, enter into 
the formation of this plexus. 
2. Derivation entirely from the para-precardinal channel, 
without involving any portion of tributary 4. 
This condition is illustrated by series 2, fig. 32,and by the dia- 
gram fig. 19. 
In this case the caudal division of the ventral veno-lymphatic 
plexus appears to be developed entirely by further growth and 
enlargement of the para-precardinal channel, without involving 
dorsal somatic tributary 4 which secondarily enters the promon- 
tory independently of the para-precardinal channel, as the first 
of the series of dorso-medial branches draining into this segment 
of the venous system. 
Here the caudal division of the ventral veno-lymphatiec plexus 
follows absolutely the developmental path of the dorsal veno- 
lymphatic plexus. 
In connection with these two main genetic types of development 
two conditions have been observed by us which are worthy of 
special mention. 
(a.) In one ease (fig. 20, diagram) the veno-lymphatic (4VL) 
and somatic (4S) elements of tributary 4 separate completely by 
