Development of the Jugular Lymph Saes. 185 
however. The second segment of the chain, proceeding posteriorly, 
extends to the fifth nerve. It equals the internal jugular vein in diameter, 
and is closely applied to its wall. Behind the third nerve it sends a blind 
diverticulum around the ventral end of the dorsal body muscles, into 
the deep subcutaneous tissue of the back. This diverticulum, not matched 
on the opposite side of the embryo, contains blood which apparently 
entered it from rough treatment in preserving the specimen. The third 
segment of the chain, between the fifth and sixth nerves, seems to connect 
with the root of the ulnar vein. This connection, however, lies in the 
plane of section, and a thin intervening wall may have been carried away 
in the process of cutting. A detached lymph space follows the dorsal 
root of the ulnar vein. A small and somewhat questionable one, not 
matched on the opposite side, rests against the superior vena cava between 
the roots of the ulnar vein. The most significant structure found in 
this embryo is a space filled with blood, which opens into the external 
jugular vein near its junction with the internal jugular. This space lies 
quite near the third segment of the lymphatic chain. On the opposite 
side of this embryo, and in the following one, this blood-filled sac con- 
necting with the vein appears to be replaced by a lymphatic space, 
detached from the vein, but connecting with the chain (p. 99). 
Concerning the next oldest stage he states that 
Fig. 3, from an embryo of 14 days, 11 mm., shows the fusion of all the 
lymphatics of the previous stage into one large sac which encircles the 
external jugular vein. On neither side could this sac be seen to communi- 
eate with the vein (p. 99). 
Upon stages older than those mentioned above he made the 
following observations concerning the relations of the jugular 
lymph sacs to the veins: 
In a 14.5 mm. rabbit (14 days, 18 hours) he found that 
on the right side of the embryo, in one section (No. 476), a minute 
orifice connected the sac and the vein. It was not in the position of 
the adult opening between these structures, and was not matched on 
the opposite side (p. 101). 
In a 20-(21)mm. pig embryo he states that “no connection be- 
tween the jugular sac and the veins could be detected”’ (p. 103). 
