284 George 8S. Huntington and Charles F. W. McClure. 
municates with the lateral surface of the promontory, through the 
subelavian approach, by a single opening (Tap C). This point of 
communication lies between the openings into the promontory of 
the cephalic and primitive ulnar veins and corresponds in its 
position and relations to a promontorial communication of the 
dorsal plexus observed in series 102 and 101 (Tap C, figs. 44, 46, 
and 49). In addition to this promontorial communication the 
dorsal plexus still retains a connection with the primitive ulnar 
vein and also communicates with the caudal division of the ven- 
tral veno-lymphatic plexus by a narrow transverse channel. Cau- 
dally the dorsal plexus of the left side (fig. 51) receives the primi- 
tive ulnar veno-lymphatic which is now completely separated 
from the primitive ulnar vein. The latter, however, has retained 
its original connection with the dorsal plexus, but has differentiated 
from the posteardinal and promontory except at its anterior end 
where it arches over the sixth spinal nerve (SP. N.V/J, fig. 51). 
On the left side (fig. 51) the caudal division of the ventral veno- 
lymphatic plexus consists of a single sac which, as mentioned above, 
communicates by a narrow channel with the dorsal plexus and by 
a single opening (Tap B) with the lateral surface of the promon- 
tory near the union of the latter with the cephalic vein. ‘This 
poitt of communication with the promontory (Tap B) corresponds, 
approximately, in its position and relations to the promontorial 
communication of the ventral plexus observed in series 102, 112 
and 101 (Tap B, figs. 44, 46, 47, 49 and 50), and the portion of the 
ventral plexus directly involved in the communication consti- 
tutes that portion of the future jugular lymph sae which we have 
termed the “jugular approach.” By tracing back its relations to the 
promontory in the above mentioned series, it will be seen that the so- 
called ‘jugular approach’ has its origin in the para-precardinal 
channel of earlier stages and that the communication at Tap B repre- 
sents one of the persistent openings by which the para-precardinal 
channel and its associated veno-lymphatic component of precardinal 
tributary 4 communicates with the promontory. 
The caudal division of the ventral veno-lymphatic plexus, as 
mentioned above, has assumed a characteristic form which appears 
to precede its fusion with the dorsal plexus. It is composed of a 
