290 George 8S. Huntington and Charles F. W. McClure. 
tical points occupied in the earlier stages by the terminals of the 
ventral and dorsal veno-lymphatic plexuses, it appears much more 
reasonable to assume a continuity of the channels throughout 
development. The picture afforded by the proper stages is, 
however, so definite and conclusive, that it becomes necessary to 
accept this separation as a normal feature of the pre-lymphatic 
stage, and as differentiating it sharply both from the earlier veno- 
lymphatic condition and from the later stage in which the definite 
secondary lymphatico-venous taps are established. 
Series 78, 12°" Embryo 
Reconstruction of left side, 
Lateral aspect, fig. 57 
The left side of this embryo illustrates an extremely important 
and evidently very evanescent stage in the transferal of the veno- 
lymphatic sac to the definite lymphatic system as the jugular 
lymph sac. It has already been referred to in connection with 
the significance of the conditions shown by series 101 and 77 (figs. 
50, 51 and 52) in which an anterior tap of evacuation was observed 
for the first time. 
The main features furnished by the left side of this embryo are 
as follows: 
1 The three primary divisions of the veno-lymphatic plexus of 
earlier stages (figs. 12 and 49) have fused with one another to form 
a common sac (fig. 57). As compared with series 77 (fig. 52), the 
relations of the spinal nerves and thyro-cervical artery to the 
resulting capacious sac elearly indicate the role played by the three 
primary divisions of the veno-lymphatic plexus in forming the sac. 
2 The primary promontorial connections of earlier stages, 
which exist between the venous system and the plexus (Taps Bb 
and C, figs. 51 and 52) at the jugulo-subclavian and ecmmon 
jugular angles, have been completely lost as far as can be deter- 
mined by the most careful observations. The jugular and sub- 
clavian approaches, however, form prominent processes of the sac, 
and terminate blindly near the point where they formerly com- 
municated with the lateral surface of the promontory (fig. 51, 11 
