296 George 8. Huntington and Charles F. W. McClure. 
3. The entire dorsal arch is derived from the dorsal veno- 
lymphatic plexus and the veno-lymphatic components of the 
precardinal tributaries, and terminates caudally in a pointed 
extremity (subclavian approach), which is directed toward the 
jugulo-subclavian angle, near which it forms a doubtful connection 
with the venous system (slide E, sections 197-198). 
4. The primitive ulnar lymphatic, derived from the primi- 
tive ulnar veno-lymphatic. This structure now contains no blood 
cells, is distinctly lymphatic in structure, and forms a blind ap- 
pendage to the caudal end of the jugular sac, arching dorso- 
ventrad over the brachial plexus, the sixth spinal nerve of which 
is represented in the figure SP. N. VJ. 
These components of the jugular lymph sac can readily be 
homologized with their equivalents in series 102, (fig. 46), series 
101 (fig. 49), series 77(fig. 51) and series 78 (fig. 57). 
The relations of the spinal nerves to the jugular lymph sac in 
the 10.7 mm. embryo remain fundamentally the same as in the 
later veno-lymphatice and pre-lymphatic stages and may be com- 
pared with those in figs. 49, 50, 52 and 57. 
The external jugular terminal which opens singly into the pro- 
montory in series 102, (fig. 46), has united with the base of the ceph- 
lic vein, forming the common jugulo-cephalic trunk so character- 
istic of later stages. 
In this, as well as in all subsequent stages, the promontory is no 
longer recognizable as an expanded and dilated portion of the 
main venous channel, but its former position is easily determined 
by the relations of the thyro-cervical artery and by the presence of 
a series of dorsal somatic tributaries which open into the jugular 
vein near the caudal end of the jugular lymph sac. These tribu- 
taries have been fully described in connection with the preceding 
stages (see 4S, 5S, 6S, 7S and 88, fig. 45). 
Reconstruction of Right side, Lateral A spects (slides C, D, andE), Fig. 59. 
The right side of this embryo presents identically the same con- 
ditions as the left, including the presence of a doubtful lymphatico- 
venous connection near the jugulo-subelavian angle (slide # 
section 194), with the exception that the cephalic and caudal divis- 
