236 «George S. Huntington and Charles F. W. MeClure. 
compared with the preceding series 30 and 31, has been developed 
as the result of the formation of the elongated fenestra Y (figs. 27 
and 28), by means of which a dorsal para-precardinal channel has 
become separated from the main precardinal vein in the area 
between the promontory and the primary precardinal connection 
(X) of tributary 4 (fig. 27, X). This para-precardinal channel may 
have been formed as the result of the caudal extension along the 
precardinal of a fenestral process in the terminal of tributary 4, 
similar to that present in series 30 (fig. 28). 
It is not possible to state definitely what the subsequent fate of 
tributary 4 and its associated para-precardinal channel would 
have been in this specific instance, if the embryo had continued to 
develop. Tributary 4 would, however, be potentially capable of 
separating into a dorsal somatic (48 in fig. 11A) and a veno- 
lymphatic component (4VL in fig. 11A), the former opening into 
the promontory as the first of the series of promontorial somatic 
tributaries, and the latter entering into the formation of the caudal 
or posterior division of the ventral veno-lymphatic plexus, as well 
as contributing to the forward extension of the dorsal veno- 
lymphatic plexus (fig. 13). 
The promontory is a capacious sac, formed largely by the di- 
lated proximal end of the postcardinal vein and is continued 
ventrally into the duct of Cuvier. The dorso-medial aspect of 
the promontory and of the postcardinal vein receives at regular 
intervals the dorsal somatic tributaries 5S, 6S, 7S, and 8S (fig. 28, 
medial aspect). J 
The dorso-lateral aspect of the promontory (figs. 27 and 28) 
presents a most typical picture of the redundant venous develop- 
ment of this stage. It is occupied by an elongated capacious and 
fenestrated sac (dorsal veno-lymphatic plexus) in wide open com- 
munication with the main vein, continued caudad into the anlage 
common to the primitive ulnar vein and the primitive ulnar veno- 
lymphatic. A series of five fenestrae run along the junction of the 
dorsal veno-lymphatie plexus and the promontory at irregular 
intervals, and are continuous with those which separate the anlage 
common to the primitive ulnar vein and veno-lymphatie from the 
posteardinal. 
