Development of the Jugular Lymph Sacs. 247 
somatic precardinal elements, but with a number of communications 
still persisting between the corresponding elements of the two sets. 
Precardinal dorsal tributary 1 is fenestrated at its junction 
with the main vein, so as to open into the same by two inter- 
fenestral channels (1VL, fig. 35). It occupies the dorso-lateral 
aspect of the vein aad may be fairly regarded as the most ante- 
rior veno-lymphatic element. There is no corresponding dorso- 
medial or somatic branch. 
The dorsal precardinal tributary 2 is represented by a dorso- 
lateral, dilated veno-lymphatic (2VL), which opens dorso-laterally 
into the precardinal vein (fig. 35), by two small detached veno- 
lymphatics (2VL’, figs. 35 and 36), and by a small dorsal 
somatic branch (28, fig. 36) which opens dorso-medially into the 
precardinal. 
The precardinal dorsal tributary 3 is still in the plexiform con- 
dition, and although it has not as yet divided into separate and 
independent veno-lymphatic (3VL) and dorsal somatic (3S) com- 
ponents, as in the case of tributary 2, these components can be 
clearly differentiated from each other on account of the relations 
which they bear to the dorso-lateral (3VL) and dorso-media! (3S) 
circumference of the precardinal vein (figs. 35 and 36). 
The two detached vascular elements which lie dorsal to the area 
of tributary 2, on account of their dorso-lateral position, are veno- 
lymphatics and have probably seen separated from the veno- 
lymphatic component of tributary 3. 
All of these veno-lymphatic components of tributaries 1, 2 and 3 
constitute the anlage of the cephalic division of the ventral veno- 
lymphatic plexus (cf. figs. 11 and 12). 
In the area of the complex formed by the precardinal tributary 
4 and its associated para-precardinal channel (caudal division of 
the ventral veno-lymphatic plexus) we encounter an excellent 
example of the incomplete separation between the veno-lymphatic 
and dorsal somatic components into which the early complex has 
subdivided, as the two sets of components are still connected with 
each other by means of a number of transverse vessels. 
The dorso-lateral veno-lymphatic component of tributary 4 (4VL, 
fig. 35) appears as an extensive sac, which ends anteriorily in a 
