Development of the Jugular Lymph Sacs. 265 
The cephalic division of the ventral plexus has been formed by 
tributary 1 (1VL) and from the area of the precardinal which 
receives dorsal tributaries 2 and 3 (2VL and 3VL), the latter 
two having retained their original precardinal terminations. 
The caudal division of the ventral veno-lymphatic plexus is a 
capacious and multi-fenestrated sae which lies dorso-lateral to the 
precardinal and for the most part in front of the promontory. It 
is continuous in front with the anterior division of the ventral 
plexus and communicates with the promontory by two well-de- 
fined apertures: one, the smaller of the two, being situated near 
the promontorio-precardinal angle on the lateral surface (Tap B, 
fig. 44), and the other (Tap D, fig. 44) on the cephalic surface of 
the promontory in close association with the promontorial end of 
the dorsal somatic tributary 4 ( 4S, fig. 45). 
This capacious sac which constitutes the caudal division of the 
ventral veno-lymphatic plexus has been formed as the result of a 
further development of a condition similar to that found in series 
109 (fig. 30), series 2 (fig. 32) or series 19 (fig. 41), and has been 
derived either from a para-precardinal channel or from a para-pre- 
cardinal channel.in connection with a veno-lymphatic component 
derived from precardinal tributary 4. 
Although we know, in general, the elements which may enter 
into the formation of the ventral plexus, on account of the vari- 
ability of the process, it is extremely difficult to determine defi- 
nitely in all cases of advanced stages exactly how its formation 
has been brought about. In view of the intimate relations which 
exist between this plexus and the first of the promontorial dorsal 
somatic tributaries (4S) which was derived from precardinal trib- 
utary 4, we are inclined to believe that in this case the veno- 
lymphatic component of the latter as well as the para-precardinal 
channel have entered into its formation. 
The dorsal veno-lymphatic plexus is represented by a pouch- 
like fenestrated sac which was derived from the dorso-lateral 
aspect of the promontory. It projects forward, dorsal to the 
caudal division of the ventral veno-lymphatic plexus, and now 
communicates with the promontory by only a single narrow open- 
ing (Tap C, fig. 44) near the former’s point of confluence with the 
