Frederic T. Lewis — 103 
finally some irregular spaces behind the aorta, probably derived from the 
azygos veins. These spaces also fuse across the median line at several 
points. 
The jugular sae is shaped like a D of which the chief portion is vertical 
and closely applied to the internal jugular vein. Through the aperture 
in the D pass the third, fourth, and fifth cervical nerves, and from its 
dorsal arch several deeply subcutaneous sprouts pass off, corresponding 
with the single large sac of the rabbit. No connection between the 
jugular sac and the veins could be detected. Except for this point, the 
reconstruction agrees with, and combines, the figure and diagram pre- 
sented by Prof. Sabin in this journal, Vol. 3, p. 184, and Vol. 4, p. 359. 
It does not agree so well with the diagram on p. 380 of Vol. I. In the 
latter the subeardinal lymph spaces are not shown. The posterior portion 
of the body contains instead two “ lymph hearts” arising from the pos- 
terior cardinal veins “below the Wolffian body” but anterior to the 
femoral vein. In later stages, outgrowths from these hearts invade the 
skin of the back, and ultimately, as has already been noted, Prof. Sabin 
considers that the hearts become transformed into lymph nodes. From 
this description, it appears that the posterior lymph hearts are in the 
position of the ilio-lumbar veins. In the pig embryo represented in lig. 
5, however, no lymphatics were found in relation with the ilio-lumbar 
vessels. 
Considering its lymphatic development the pig of 21 mm. is less ad- 
vanced than the rabbit of 14.5 mm., since there are no lymphatic vessels 
along the external mammary vein nor in the mesentery. The cat of 
15 mm. is more advanced than either. In this embryo the D formed by 
the jugular sac is almost bisected diagonally. The second, third, and 
fourth nerves pass through its aperture, but the fifth penetrates the 
posterior section of the sac by a separate opening. ‘There are two deep 
subeutaneous diverticula corresponding with the single one in the rabbit 
and several in the pig. In one section (266) a branch of the jugular 
sac may enter the innominate vein a little anterior to the subclavian, but 
it is not clear that an actual opening exists and none can be found on 
the opposite side. 
Where the external mammary vein joins the brachial there is a large 
sac, and the question arises whether or not the detached lymphatics fol- 
lowing the mammary vein are independent formations, or are outgrowths 
from that sac. The occurrence of the lymphatics especially near the 
places where the veins branch suggests that they may have budded at such 
points. On the other hand, as in the rabbit, their order of appearance 
is from the proximal part of the vein distally. Similarly there are 
