278 George 8. Huntington and Charles F. W. McClure. 
multiple connections with the precardinal and promontory and 
retained only one which corresponds, approximately, to the pri- 
mary point of connection of the para-precardinal channel with 
the promontory. This point of connection, as mentioned above. 
is one of the last to be given up, and also corresponds, approxi- 
mately, in its position to that of the common jugular tap in the 
adult (cf. fig. 1, left side). 
Just dorsal to the entrance of the cephalic vein into the lateral 
surface of the promontory, the thyro-cervical artery passes ventro- 
laterad in the interval between the ventral and dorsal divisions of 
the veno-lymphatic plexus. 
The dorsal veno-lymphatic plexus is now a very extensive 
structure which extends from the region of the promontory, as 
far forward as the level of the cephalic arch of the precardinal 
where it ends blindly. In the region of the promontory the dorsal 
plexus is still broadly confluent with the anlage common to the 
primitive ulnar vein and primitive ulnar veno-lymphatic which 
has not as yet separated into its two components. The line of 
cleavage along which the separation will take place, however, is 
clearly indicated by a row of fenestrae which will subsequently 
become confluent. (Compare with fig. 47). 
Just in front of its connection with the primitive ulnar arch 
the dorsal plexus gives off a ventrally directed tongue-shaped 
process (subclavian approach) which communicates with the prom- 
ontory by a single opening (Tap CY and which les near the en- 
trance into the promontory of the primitive ulnar vein. This 
point of communication with the promontory corresponds in all 
respects to that previously described for this plexus in connection 
with series 102 (Tap C, figs. 44 and 46). 
This extensive development of the dorsal veno-lymphatic 
plexus is the result of a forward growth of the redundant plexi- 
form area of the promontory and convexity of the primitive ulnar 
arch and inclusion within the same of detached veno-lymphatics 
which have been derived from the dorsal tributaries of the pre- 
cardinal. 
The fifth spinal nerve (SP.N.V) penetrates the dorsal plexus, 
while the sixth (SP.N.VJ), and following spinal nerves in this 
a 
