258 George 8. Huntington and Charles F. W. McClure. 
pathway has developed a large dilated veno-lymphatie sac 
representing the dorsal veno-lymphatie plexus. It forms an 
irregularly quadrilateral dilated and diverticular appendage, 
projecting from the dorso-lateral aspect of the promontory and 
primitive ulnar arch. The persistent pathways between the 
fenestral spaces furnish four channels of communication between 
this veno-lymphatic sac and the permanent vein. Only three 
of these channels are shown in the figure. This represents an 
advance over the conditions shown in the earlier stages in this 
region. The fenestrae have become elongated, thus drawing out 
the persistent patent intervals between them into definite and 
well-marked channels of communication. At a later stage of 
development, and in connection with the formation of the primi- 
tive ulnar veno-lymphatic, the dorsal veno-lymphatic plexus, 
through confluence of its fenestrae, becomes separated from the 
primitive ulnar vein, but retains a single point of communication 
with the promontory near the latter’s junction with the primitive 
ulnar vein (see Tap C, figs. 40 and 44). 
As previously stated, this embryo offers a marked example of 
the fact that veno-lymphatic development does not proceed uni- 
-formly in all parts in the primary venous area involved, and that 
in individual portions of this area one segment may be develop- 
mentally much in advance of the rest, in a given stage. Thus 
in the present instance the dorsal veno-lymphatic plexus is 
considerably further developed than the ventral division (para-pre- 
vardinal channel), while in other examples the reverse may obtain 
(series 2, fig. 32). The reconstruction of this embryo also fur- 
nishes a marked instance of the multiple openings, characteristic 
of the intermediate stages, between the anlages of the future defin- 
ite veno-lymphatic plexus and the permanent veins. With 
the more complete separation of the veno-lymphatic sac from 
the main venous channels the intervals between the individual 
fenestral spaces elongate and become drawn out into narrower and 
longer branches of communication between the two vascular areas. 
Thus, in the present instance, we find, caudal to the junction of 
tributary A—B with the cephalic arch, ten distinct openings lead- 
ing from the anlages of the veno-lymphatic plexuses into the dorsal 
circumference of the precardinal vein and promontory (fig. 40). 
