228 George 8. Huntington and Charles F. W. McClure. 
Series 30, 5-+"""" Embryo 
Reconstruction of right side, 
Lateral aspect, fig. 23 
A—B, as the main dorsal branches of the cephalic arch, occupy 
relatively the same position as on the left side. They are 
reversed in size, A representing the main drainage channel, while 
on the left side B is the larger of the two vessels. 
The anterior precardinal spindle J (fig. 23, I) is well marked. 
A small fenestra in the dorsal portion of spindle J may represent 
the beginning separation of the element B', which on the left 
side forms a dilated appendage to B. 
Dorsal tributaries 1, 2 and 3 are single and distinctly defined. 
1 and 2,as on the left side, are closely approximated, so that pre- 
cardinal spindles J and J/ are practically confluent. ~ Precardinal 
spindle JV is well developed. It receives dorsally tributary 3. 
Spindle V is not pronounced, the dilatation at this point being 
taken up by the marked enlargement of the terminal of dorsal 
tributary 4. The broad quadrilateral channel formed by the 
confluence of its cephalic and caudal tributaries is fenestrated at 
the junction with the precardinal so that the tributary enters the ~ 
main vein by an anterior and posterior trunk. This fenestra 
represents the space framed by the venous arch which 4 in the 
later veno-lymphatic stages so frequently forms at its junction 
with the main vein, and its presence denotes the beginning for- 
mation of a reticular and fenestrated complex by means of which, 
as above defined, this tributary may become connected with the 
promontory in the later stages. From our reconstruction of these 
later stages it is evident that its transferal to the promontory 
may take place in one of two ways: | 
(a) The anterior of the two trunks forming the terminal of . 
4 may retain its connection with the precardinal vein, and the 
posterior trunk may travel back, along the line of the fenestrated 
reticulum, to the promontory, in which case the arch frames 
dorsally a vertical parajugular foramen (figs. 27, 30 and 31) or, (6) 
both trunks may become thus secondarily drained into the pro- 
montory, in which case a closed venous arch projects forward 
from the anterior face of the promontory (fig. 38). 
