BLOOD AND VITELLINE VESSELS IN AMPHIBIA 303 
A wax reconstruction was made of the vessels and heart of a 
22 somite embryo, 6 mm. in length (figs. 12 and 13). There were 
some difficulties in determining the exact extent of the blood 
spaces and the size of some parts may be exaggerated, especially 
some of the somatic vessels... The heart is shown as a twisted 
tube connected with a single aortic arch, from the forward part 
of which only two small branches arise. The aorta runs back 
some distance, with lateral branches, the vitelline arteries, commu- 
nicating with the yolk spaces. Only one pair of these is shown. 
Just how many of these arteries there were was hard to determine. 
Fig. 12 Caudal view of a model of the vascular system of Amblystoma puncta- 
tum 6 mm. long, 22 somites. The caudal end of the heart or sinus venosus (s) 
is shown composed of a larger left side and a smaller right. Lateral to the heart 
the lateral cutaneous vessels are shown (cal). The cut aorta (a) is shown in the 
middle line. X 100. 
The veins of the head region branch to some degree and run well 
back to unite with the broad spaces or veins in the body-wall. 
These lateral vessels communicate on each side rather broadly 
with the large sinus. 
Spaces on the yolk, most of which are mere lacunae as yet, 
communicate with each other and come near the sinus on each 
side, but do not unite with it. These lacunae and beginning 
vessels also communicate at various levels with the lateral and 
ventral thickenings of the mesoderm and probably also with 
branches of the dorsal aorta in a more caudal region. 
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