252 George 8. Huntington and Charles F. W. McClure. 
sion of the veno-lymphatic plexus, which occupies a similar posi- 
tion and is so often met with in later stages (see series 77, fig. 51). 
The other veno-lymphatic component (4VL) of precardinal tribu- 
utary 4 is the larger of the two. It occupies a dorso-lateral posi- 
tion, has given up its connection with the precardinal and opens 
into the promontory by a right-angled line which is directly 
continuous with that of the dorsal veno- lymphatic plexus. 
This embryo shows a condition which can be derived from that 
obtaining in series 30 and 31 (figs. 23 and 24) by development of 
a para-precardinal channel involving the fenestrated terminal 
of tributary 4 and the subsequent detachment of the complex 
thus formed from the precardinal and promontory back to the 
point where if becomes continuous with the dorsal veno-lymphatic 
plexus. 
The right-angled limb of this veno-lymphatic structure shows 
clearly the course along which the process of fenestration pro- 
ceeded. We have here an instance, in all probability, in which the 
precardinal tributary 4 has been transformed in its entirety into 
veno-lymphatic components. If such is actually the case, dorsal 
somatic tributary 5S, as in the present case (fig. 38), will form the 
first of the promontorial tributaries. 
Veno-lymphatic formation along the dorso-lateral cireum- 
ference of the promontory and postcardinal vein is well advanced 
on the right side of this embryo except for an area which inter- 
venes between the dorsal veno-lymphatic plexus and the anlage 
common to the primitive ulnar vein and primitive ulnar veno- 
lymphatic. This anlage opens into the main channel at three 
points in the neighborhood of the termination of the promon- 
torial dorsal somatic tributary 7S (fig. 38). Caudad of these 
connections the primitive ulnar vein has completely separated 
from the posteardinal. 
The promontory is not as yet a capacious sac and is formed on 
the right as well as upon the left side (fig. 39) by the enlarged 
Cuvierian end of the posteardinal. The anlage of the external 
jugular vein opens on each side into the proximal end of the duct 
of Cuvier, a circumstance which denotes the still incomplete 
development of the promontory. 
