Frederic T. Lewis 99 
branches. One of these, nearly parallel with the dorsal border of the vein 
and wider than the others, opens into the vein at either end. It is in 
relation with the third cervical nerve. From its position and appearance 
it is beheved that this branch of the vein becomes a lymphatic vessel. 
The second reconstruction is a 10 mm. embryo of 14 days. In this 
specimen a chain of lymphatic spaces has appeared along the internal 
jugular and the dorsal root of the primitive ulnar veins. The most 
anterior segment of the chain extends back to the third cervical nerve. It 
sends out short blind sprouts like a veim and contains many blood 
corpuscles. ‘The partition between it and the jugular vein is very thin, 
and at one point there is a suggestion of communication between the 
two, as shown in the figure. No opening into the vein can be demon- 
strated, however. The second segment of the chain, proceeding poste- 
riorly, 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 divertic- 
ulum, 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, hes 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 question- 
able 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 connecting with the vein appears to be replaced by a lymphatic 
space, detached from the vein, but connecting with the chain. 
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 com- 
municate with the veins. No lymphatic vessels were found which did not 
connect with the jugular sacs. The dorsal subcutaneous extension, de- 
scribed in the preceding stage, occurred on both sides. In the posterior 
part of the embryo, no lymphatics were found. The reconstruction of 
the cardinal veins is that already figured in this journal, Vol. I, Plate 
2, Fig. 5 (following p. 244). 
