286 George 8. Huntington and Charles F. W. McClure. 
a prominent structure on the right side, its outline being indicated 
in the figure by a broken line. 
The relation of the first five spinal nerves to the veno-lymphatic 
plexusesis indicated in the reconstruction of the right side (fig. 52). 
The first and second (SP.N.J and JJ), third (SP.N.JII) and 
fourth (SP. N. IV) nerves pass ventro-laterad between the cephalic 
and eaudal divisions of the ventral veno-lymphatic plexus, and 
the fifth (SP.N.V) nerve passes directly through the dorsal 
plexus. The sixth spinal nerve (SP.N.V/J, fig. 51) lies behind 
the dorsal plexus and arches ventro-laterad under the primitive 
ulnar vein. 
The thyro-cervical artery, as in the preceding stage, lies ventral 
to the subclavian approach and between the dorsal and ventral 
divisions of the veno-lymphatic plexus. 
These relations of the spinal nerves are retained in later stages 
after the primary divisions of the veno-lymphatic plexus have 
fused to form a common sac. Subsequently, after the comple- 
tion of the veno-lymphatic process, the resulting jugular lymph 
sac divides at its anterior extremity (fig. 17), thus freeing the 
nerves, which then come to pass, first between the dorsal portion 
of the sac and the internal jugular vein, and, finally, entirely dor- 
sal to the sac. The relation of the thyro-cervical artery to the 
lymph sac is, however, retained throughout and persists in the 
adult. 
In view of the importance of the two embryos, which consti- 
tute this group (series 101 and 77), since they represent a stage of 
development which immediately precedes the establishment of 
the jugular lymph sacs, it may be well to tabulate the principal 
features which they illustrate, as follows: 
Series 191, 10°" Embryo 
Figs. 49 and 50 
1. This embryo furnishes an excellent example of the three 
main divisions of the veno-lymphatic plexus, fully developed, but 
still quite distinct from each other. 
2. The extensive forward growth of the dorsal veno-lymphatic 
plexus and the establishment, on the right side, of an anterior 
a ee ae Po 
