98 Walter E. Dandy. 
eleven lateral branches, beginning as very minute and rather indefinite 
branches posterior to the first somite; these become progressively 
larger and reach a climax at the posterior dilatation of the aorta. 
In the somite region they are solid buds (Fig. 5), the last five aris- 
ing from the dilatation have a lumen, but end blindly in the meso- 
derm of the splanchnopleure (Fig. 5). On the right side the last 
three branches seem to end in a common blood island, giving the 
impression of a small capillary plexus; this was, however, not 
ebserved on the other side. These branches probably represent the 
segmental arteries of Mall destined for the umbilical vesicle. In 
the somite region there are six of these branches for the seven 
somites; on one side all six arise between the somites; on the other 
side three arise intersegmentally, the other three come off nearer 
the center of the somites. From the dorsal and caudal end of the 
posterior aortic dilatation there is a very short stub on each side, 
which may represent the beginning of the caudal aorta. Otherwise 
no dorsal branches of the aortee were observed. 
The umbilical arteries, somewhat larger than the aorte, are 
direct posterior continuations of the posterior aortic dilatation. In 
the bauchstiel they unite to form a large sinus (Fig. 9) which lies 
posterior to the smaller venous sinus. (Fig. 8.) It sends off numer- 
ous large branches to the chorion, some of which anastomose and 
redistribute branches to the chorionic membrane and villi. 
It is a pleasure to extend my heartiest thanks to Professor Mall 
for his kindness in allowing me the privilege of describing this very 
rare specimen, for his valuable advice and suggestions and for the 
use of two manuscripts which are not yet in print. 
