218 George 8S. Huntington and Charles F. W. McClure. 
In later stages this primitive ulnar veno-lymphatie becomes 
secondarily connected with the systemic lymphatic vessels of the 
anterior extremity, in the same way in which on a larger scale, 
the thoracic duct secondarily taps the process of the jugular 
lymph sae which forms its portal of entry into the same. The 
partial separation of the common anlage of these two structures, 
viz., primitive ulnar vein and primitive ulnar veno-lymphatie, 
is shown in fig. 12. Their subsequent development can be followed 
in figs. 13 to 17 inel. 
SECOND PERIOD. 
II. From THE ESTABLISHMENT OF THE THREE PRIMARY VENO- 
LYMPHATIC PLEXUSES OR SINUSES TO THE ATTAINMENT OF 
THE ADULT CONDITION OF THE JUGULAR LymPpH Sacs. 
This period is characterized by the following well-marked char- 
acters: 
1. Further reduction of the multiple early connections between 
the veno-lymphatic plexuses and the permanent veins, and the 
consequent more complete separation of the former from the latter, 
the plexuses or sac-like structures assuming a greater degree of 
independence. ‘This general process of separation and loss of 
early communicating channels appears to proceed from both 
extremities of the area toward the jugular promontory where the 
embryonie connections are longest retained and where the two 
permanent adult communications between the lymphatics and 
the veins are established. It is to be noted, however, that in 
many observed cases the termination of one or more of the anterior 
dorsal somatic tributaries persists as an open communication 
between the cephalic division of the ventral veno-lymphatic plexus 
and the anterior part of the precardinal, and in later stages even 
enlarges considerably, forming the main veno-lymphatic-venous 
connection and functioning as the anterior tap of evacuation 
(cf. figs. 12 to 15, and series 78, fig. 57). 
2. The three primary veno-lymphatic plexuses begin to fuse 
with each other to form a common sac. 
