266 George 8S. Huntington and Charles F. W. McClure. 
primitive ulnar vein. As mentioned above, in connection with 
the description of series 106 (fig. 40), this condition has been 
reached as the result of a separation of the sac from the anterior 
end of the anlage common to the primitive ulnar vein and prim- 
itive ulnar veno-lymphatic, and by the retention of only one of 
its primary promontorial points of connection. This single tap 
(Tap C, fig. 44) corresponds, approximately, in its position to that 
of the lymphatico-venous connection of later stages which is found 
at the jugulo-subelavian junction, while the more ventrally situ- 
ated tap (Tap 2) corresponds, approximately, to that met with at 
the junction of the external and internal jugular veins. 
The thyro-cervical artery passes laterad close to the surface 
of the promontory, between the dorsal plexus and the caudal divi- 
sion of the ventral veno-lymphatic plexus. 
This artery, from this stage on, is constantly encountered in 
this position and offers a uniform relationship to the components 
of the veno-lymphatie plexus. It thus constitutes an important 
landmark in differentiating in later stages and in the adult the 
parts of the united jugular lymph sac derived, respectively, 
from the dorsal plexus and caudal division of the ventral veno- 
lymphatic plexus. 
The promontorial end of the dorsal veno-lymphatic plexus 
constitutes the subclavian approach of later stages and can al- 
ways be identified by the constant relation which it holds to the 
ventrally situated thyro-cervical artery. 
The anlage common to the primitive ulnar vein and primitive 
ulnar veno-lymphatic has separated into these two components. 
The former arches over the sixth spinal nerve (SP.N.VI) and 
opens into the dorso-lateral circumference of the promontory be- 
tween the latter’s point of confluence with the sixth and*seventh 
dorsal somatic tributaries (68 and 7S, figs. 44 and 45). The prim- 
itive ulnar veno-lymphatie is a small vessel which runs parallel 
to the primitive ulnar vein. It has been completely differentiated 
from this vein except at its anterior end where indications of its 
former connection with the same are still evident. At a later 
stage it will completely separate from the primitive ulnar vein and, 
after joining the dorsal veno-lymphatie plexus, form a caudal 
extension of the latter. 
